Dopamine agonists and pituitary tumor shrinkage.

The primary aim of this review has been to clarify the tumor shrinking effects of dopamine agonists on pituitary macroadenomas of different cell types. Shrinkage is most dramatic for macroprolactinomas and is due to cell size reduction. Seventy-nine percent of 271 definite macroprolactinomas were reduced in size by at least 25%, and 89% shrank to some degree. Most shrinkage occurs during the first 3 months of treatment, although in a minority shrinkage is delayed. Dopamine agonist resistance during long-term therapy is exceptional. Drug withdrawal nearly always leads to a return of hyperprolactinemia, even after several years treatment, although early tumor reexpansion is unusual. About 10% of true macroprolactinomas do not shrink with dopamine agonists; the molecular mechanisms of such resistance have yet to be determined. Alternative formulations of BC and new dopamine agonists (CV 205-502 and cabergoline) are useful for the minority of patients unable to tolerate oral BC, but do not seem to further improve overall shrinkage rates. The risks of pregnancy have probably been overstated, and BC is suitable primary treatment for women with prolactinomas of all sizes; the drug can be used safely during pregnancy in the event of clinically relevant tumor expansion. The interpretation of different degrees of hyperprolactinemia is discussed and management strategies suggested. Most patients with macroprolactinomas now avoid surgery, but drug-induced, time-dependent tumor fibrosis should be remembered if surgery is contemplated. Nonfunctioning pituitary tumors are mostly of gonadotroph cell origin and may be associated with significant disconnection hyperprolactinaemia. Seventy-six of 84 well-characterized tumors showed no tumor shrinkage during dopamine agonist therapy. Possible explanations include abnormalities of dopamine receptor number and function. Preliminary evidence suggests that dopamine agonists may restrain the growth of some functionless tumors; most of these tumors, however, can be satisfactorily debulked using transsphenoidal surgery. In contrast to macroprolactinomas, other functioning pituitary tumors (GH-, TSH-, and ACTH-secreting) rarely shrink during dopamine agonist therapy, although the number of tumors studied is small.

Thyrotropin-releasing hormone in the systemic circulation of the neonatal rat is derived from the pancreas and other extraneural tissues.

Thyrotropin-releasing hormone immunoreactivity (IR-TRH) has been detected in the circulation of the neonatal rat. This immunoreactivity was demonstrated in purified ethanol extracts of plasma, and was indistinguishable from synthetic TRH using radioimmunoassay and chromatographic criteria. To determine the source of the circulating IR-TRH, tissue concentrations of TRH were analyzed during maturation of the rat. These studies revealed that during the first 10 d of life, the pancreas contained the greatest concentration of IR-TRH of any organ (pancreas, 289+/-35 pg/mg; hypothalamus, 13+/-3 pg/mg, day 5). Thereafter, pancreatic IR-TRH concentrations declined progressively while hypothalamic concentrations gradually increased (pancreas, 1.2+/-0.2 pg/mg; hypothalamus, 365+/-54 pg/mg, adult rat). IR-TRH was also found throughout the gastrointestinal tract but was not detected in the liver, spleen, kidney, or heart. IR-TRH from the pancreas and gastrointestinal tract gave radio-immunoassay binding displacement curves that were parallel to a curve generated with synthetic TRH, and co-migrated with synthetic TRH on Sephadex G-10 and high performance liquid chromatography. In addition, IR-TRH from purified pancreatic extracts was biologically active in that it released thyrotropin and prolactin from rat adenohypophysial cells maintained in monolayer culture. When a total pancreatectomy was performed on the 5th d of life of the rat, mean plasma TRH concentrations were significantly decreased 3 h afterwards (84+/-9 vs. 63+/-7 pg/ml, P < 0.05). Neither the TRH concentrations in the brain, hypothalamus, or gastrointestinal tract, nor the pituitary-thyroid axis were affected by the pancreatectomy. However, mean plasma TRH concentrations remained unaltered 3 h after removal of the hypothalamus and extrahypothalamic brain. FROM THESE RESULTS WE CONCLUDE THE FOLLOWING: (a) the TRH immunoreactivity in the circulation, pancreas, and gastrointestinal tract of the neonatal rat is indistinguishable from synthetic TRH; (b) pancreatic secretion provides a significant contribution to the IR-TRH in plasma, and a proportion of the circulating IR-TRH is derived from other extraneural sites. These findings therefore imply that alterations in hypothalamic and extrahypothalamic brain secretion of TRH are not reflected by changes in levels of this tripeptide in the systemic circulation.

Pheochromocytoma in Pregnancy: When is Operative Intervention Indicated?

Pheochromocytoma is rare in pregnancy, with an estimated incidence of 0.007%. Diagnosis is difficult owing to the variety of presentations and nonspecific symptoms. Nevertheless, unsuspected disease accounts for a significant proportion of morbidity and mortality. Currently, there appears to be no consensus on management with regard to the need for and timing of medical vs. surgical management. In this case report, we describe two patients who underwent different modes of treatment based on careful consideration of disease-related and nondisease-related factors. We emphasise that good outcomes can be achieved through individualized management within the context of a multidisciplinary team, involving close collaboration among physicians, surgeons, obstetricians, and anesthetists. We also illustrate the importance of genetic testing in all patients with pheochromocytoma in pregnancy, especially with the emergence of new predisposing genes (succinate dehydrogenase B and D) and the recognition that germline mutations in these and more established genes (VHL and RET) account for over a quarter of all apparently sporadic cases.

Growth factors and pituitary tumors.

Growth within the anterior pituitary gland is probably controlled by several interacting extracellular messenger molecules, including hypothalamic peptides, target gland hormones, and several growth factors acting in autocrine or paracrine fashion. Adenoma formation may result from abnormal production of such factors or their specific cellular receptors, loss of local inhibitory influences, activation of the intracellular secondary message pathways conveying the mitogenic signal to the nucleus, or deregulation of the nuclear processes controlling mitosis.

Are factors at diagnosis of growth hormone deficiency in childhood associated with persistence of growth hormone deficiency into adult life?

A proportion of children with growth hormone deficiency (GHD) have persistence of GHD as young adults. To date, no markers have been shown in childhood to have predictive value in determining persistence of GHD into adult life. We examined the hypothesis in 31 patients that variables present at the time of diagnosis of childhood-onset GHD, or those related to the early response to growth hormone (GH) therapy, are associated with the likelihood of persistence of GHD. The results show that, as previously demonstrated, children with GHD are more likely to have persistent severe GHD in adult life when the diagnosis is associated with other pituitary hormone deficiencies (p = 0.02), abnormal pituitary neuroimaging (p = 0.003), induced puberty (p = 0.001), early age of diagnosis (p = 0.03) and lower peak GH response at the first dynamic GH test in childhood (p = 0.02). However, there are no associations of persistent severe GHD with the pattern of pretreatment growth or growth response to GH treatment in the initial phase.

Early-morning hyperglycemia in IDDM. Acute effects of cholinergic blockade.

Growth hormone (GH) hypersecretion in insulin-dependent diabetes mellitus (IDDM) subjects has been shown to be causally related to early-morning hyperglycemia. We studied the effect of nocturnal GH suppression on acute glycemic control in six IDDM patients during a constant overnight insulin infusion (0.075 mU.kg-1.min-1). In control experiments (infusion of insulin alone), plasma glucose increased from 5.6 +/- 0.6 mM at 2400 to 11.1 +/- 1.3 mM at 0900 (P = .0024). When in addition the cholinergic muscarinic antagonist pirenzepine was given (100 mg at 2200 and again at 2400), plasma glucose increased from 5.6 +/- 0.3 mM at 2400 to 8.4 +/- 1.4 mM at 0900 (P greater than .05). The nocturnal surges of GH that were demonstrated in all patients during the control nights were suppressed during the treatment nights. There were no significant changes in insulin, cortisol, or epinephrine concentrations. Mean glucagon and norepinephrine concentrations. Mean glucagon and norepinephrine concentrations were reduced from 127 +/- 2.7 ng/L and 8.7 +/- 0.5 nM to 101 +/- 1.9 ng/L (P less than .001) and 3.5 +/- 0.2 nM (P less than .001) on control and treatment nights, respectively. Neither glucagon nor norepinephrine concentrations changed significantly between 2400 and 0900 on either control or treatment nights. We conclude that nocturnal GH suppression by pirenzepine during a constant low-rate insulin infusion is associated with an attenuation of the early-morning plasma glucose rise.

Hypothyroid pituitary cells in culture: an analysis of thyrotropin and prolactin responses to dopamine (DA) and DA receptor binding.

Monolayer cultures were prepared from the anterior pituitary (AP) lobes of normal male rats and male rats made hypothyroid by treatment with aminotriazole. After 3 days in culture, the cells from hypothyroid animals showed significantly greater TSH and PRL secretory activity and significantly less GH secretory activity than did parallel euthyroid cultures. The responses of euthyroid and hypothyroid cultures to dopaminergic agonists and antagonists were examined. Bromocriptine, apomorphine, and dopamine (DA) inhibited euthyroid TSH secretion by approximately 30%, whereas each drug inhibited hypothyroid TSH secretion by approximately 60% (P less than 0.01 for each drug). In contrast, the three agonists were less effective in inhibiting PRL secretion from hypothyroid cells (P less than 0.05 for each drug). The rank order of potency [bromocriptine greater than (+)butaclamol greater than apomorphine greater than DA greater than (-)butaclamol] shown against secretion was the same for TSH and PRL in both euthyroid and hypothyroid cell cultures and is typical of a DA receptor-mediated process. The binding of [3H]dihydroergocryptine (DHE) to DA receptors on euthyroid and hypothyroid cells was examined under the same conditions in which the secretory responses were determined. One micromolar concentration of (+)butaclamol was used to define nonspecific binding. Specific binding was saturable and stereospecific in each case. The rank order of potency of dopaminergic agonists and antagonists in competing for [3H] DHE binding was the same as that demonstrated against the secretion of TSH and PRL. Each compound displaced significantly more [3H]DHE from hypothyroid cells than from euthyroid cells (P less than 0.05 for each drug). Construction of adsorption isotherms for [3H]DHE binding to DA receptors on euthyroid and hypothyroid cells and subsequent Scatchard analysis revealed a 3- to 4-fold increase in receptor number without a significant change in affinity. Immunohistochemistry on AP lobes before and after dispersion revealed an increase in thyrotrophs and thyroidectomy cells in hypothyroid rats relative to those in control animals. In euthyroid animals thyrotrophs were 10.1% of the total AP cell population, in hypothyroid animals they plus the thyroidectomy cells were 36.3% of the total AP cells. Therefore, the increased number of DA receptors per lobe could be accounted for by increased numbers of thyrotrophs. The mechanism of the altered sensitivity to DA induced by hypothyroidism in lactotrophs and thyrotrophs remains to be clarified.

Alpha 1-adrenoreceptors on intact rat anterior pituitary cells: correlation with adrenergic stimulation of thyrotropin secretion.

An in vitro study of the alpha-adrenergic control of TSH secretion was carried out on rat anterior pituitary cells in monolayer culture. The ability of adrenergic agonists and antagonists to alter TSH release from the cells was determined. With the use of parallel cell cultures under the same conditions, alpha-adrenergic binding sites were measured and characterized with [3H]dihydroergocryptine (DHE) as the radioligand. Epinephrine (E) and norepinephrine (NE) released TSH over a 2-h period in a dose-dependent and stereospecific manner (ED50 = 1 and 700 nM for the (-) and (+/-) stereoisomers of E; 7 and 600 nM for the active and inactive stereoisomers of NE respectively). Maximum release was 3- to 4-fold greater than basal secretion for both isomers of E but less (2- to 3-fold) for the isomers of NE. Phenylephrine, an alpha 1-agonist, elicited a 2- to 3-fold increase in TSH secretion (ED50 = 13 nM). Clonidine, an alpha 2-agonist, produced only slight stimulation at concentrations greater than 10(-6) M, and isoproterenol was ineffective. Prazosin, an alpha 2-antagonist (IC50 = 0.12 nM), was 500-fold more effective than yohimbine, an alpha 2-antagonist (IC50 = 60 nM), in reversing the TSH stimulation induced by 10(-7) M E. With [3H]DHE and prazosin as competing ligands, alpha-adrenergic receptors could be quantified independently of dopamine receptors present upon the same mixed cell preparations. The kinetics of specific radioligand binding to the cells were rapid (k1 = 1.75 X 10(-7) M-1 min-1, k2 = 0.131 min-1), equilibrium being reached within 15 min at 22 C. Adsorption isotherms and Scatchard analysis revealed a single population of binding sites with high affinity (kd = 7.2 nM) and low capacity (3 fmol/10(5) cells). Competition by adrenergic agonists for [3H]DHE binding was stereospecific. The rank order of potency against binding was identical with that determined functionally against TSH secretion (Ki for prazosin, 0.7 nM greater than thymoxamine, 2.7 nM greater than (-) E, 7 nM greater than phentolamine, 8 nM greater than (-) NE, 11.5 nM greater than phenylephrine, 100 nM greater than yohimbine, 300 nM greater than clonidine, 4500 nM greater than (+/-) E, 5000 nM greater than (+/-) NE, 7000 nM greater than isoproterenol, 3 X 10(5) nM), and typical of binding to an alpha 1-adrenoreceptor. It is concluded that TSH can be specifically released from rat anterior pituitary cells in monolayer culture by the direct effects of adrenergic agonists and that the stimulation is mediated via a single high affinity population of alpha 1-adrenergic receptors.

The effects of thyroid hormone deprivation in vivo and in vitro on growth hormone (GH) responses to human pancreatic (tumor) GH-releasing factor (1-40) by dispersed rat anterior pituitary cells.

Anterior pituitary cells from euthyroid and hypothyroid male rats have been cultured as monolayers for 3 days with or without 5 nM T3 and stimulated with either human pancreatic GH-releasing factor 1-40 (hpGRF), TRH, or the Ca2+ channel ionophore A23187. Basal GH secretion was reduced in the hypothyroid cultures (P less than 0.001) and basal TSH secretion increased (P less than 0.001). Culture with T3 increased GH secretion and intracellular GH content in euthyroid and hypothyroid cultures but suppressed TSH secretion with no effect on intracellular TSH content in either euthyroid or hypothyroid cultures. hpGRF released more GH from euthyroid [3.52 +/- 0.2 (SE) micrograms/6 h X 10(5) cells] than hypothyroid cultures of (0.17 +/- 0.01 micrograms/6 h X 10(5) cells, P less than 0.001) without a change in ED50 (approximately 0.02 nM). The reduction in hpGRF-induced GH release remained significant when corrected for the reduced intracellular GH content in the hypothyroid cultures. hpGRF-induced GH release also declined relative to A23187-induced GH release in hypothyroid cultures. Culture with 5 nM T3 doubled maximum hpGRF-induced GH release in euthyroid cultures and increased maximum release 10-fold in hypothyroid cultures without altering the ED50 of hpGRF action. In contrast, T3 suppressed TRH-induced TSH release in euthyroid cultures but was without effect on TRH-induced TSH release in the hypothyroid cultures. T3 did not effect the ED50 of TRH action (2-5 nM). In summary, hypothyroid rat anterior pituitary cells in culture have a reduced maximal GH response to hpGRF, but the same ED50. hpGRF activity can be partially restored by physiological concentrations of T3 in vitro.

Alpha 1-adrenoreceptors and alpha 1-adrenoreceptor-mediated thyrotropin release in cultures of euthyroid and hypothyroid rat anterior pituitary cells.

TSH responses to adrenergic agonists have been measured in 3-day monolayer cultures of euthyroid and hypothyroid male rat anterior pituitary (AP) cells. Responses were qualitatively similar in that (-)epinephrine and (-)norepinephrine had the same ED50 in each culture (ED50 = approximately 6 and 16 nM, respectively) and demonstrated the same alpha 1-adrenergic specificity. Hypothyroid cultures secreted approximately twice as much TSH per cell as euthyroid cultures over the 2-h experimental period. (-)Epinephrine produced a 95 +/- 8% (mean +/- SE) release of TSH relative to basal secretion in euthyroid cultures and only 62 +/- 7% release in the hypothyroid cultures (P less than 0.01). The comparable figures for (-)norepinephrine were 62 +/- 7% and 38 +/- 5%, respectively (P less than 0.05). In absolute terms, adrenergic agonists released the same amount of TSH from euthyroid and hypothyroid cultures. In contrast, TRH (and the Ca+2 channel ionophore A23187) released twice as much TSH from the hypothyroid cells as in the euthyroid cultures. Epinephrine-induced TSH release was significantly impaired (P less than 0.001) when either euthyroid or hypothyroid cells were cultured without thyroid hormones. In contrast, TRH-induced TSH release was enhanced (P less than 0.001) in the euthyroid cultures. [3H]Dihydroergocryptine [( 3H]DHE) was used to quantify alpha 1-adrenoreceptors on the same cell preparations as those used to derive the functional data (see above). Prazosin (1 microM) was used to define nonspecific binding of [3H]DHE. Specific binding to euthyroid cells had a Kd of 5.8 +/- 4 nM and a maximum binding capacity of 2.2 +/- 0.4 fmol/10(5) cells (n = 5). In parallel cultures of hypothyroid cells, the Kd (6.2 +/- 5 nM) was not significantly different, whereas the maximum binding capacity (1.4 +/- 0.3 fmol/10(5) cells) was significantly reduced (P less than 0.05). Adrenergic compounds showed a rank order of potency of prazosin greater than (-)epinephrine greater than or equal to (-)norepinephrine greater than or equal to yohimbine greater than clonidine against the binding of 5 nM [3H]DHE to euthyroid and hypothyroid cells. The amount of [3H]DHE binding per cell that each adrenergic compound was able to displace at saturating concentrations was less in hypothyroid cells than in euthyroid cells. There was no change in the ED50 values of these compounds in the same experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Interactions among epinephrine, thyrotropin (TSH)-releasing hormone, dopamine, and somatostatin in the control of TSH secretion in vitro.

Epinephrine and TRH independently release TSH from rat anterior pituitary cells in primary monolayer culture (ED50, 11 and 5 nM, respectively; maximum responses, 80% and 110%, respectively). The effects of these compounds together are additive, even at concentrations at which each is maximally effective alone. Dopamine inhibited basal and epinephrine-stimulated TSH secretion by 25 +/- 5% (+/-SE; ED50, 50 +/- 9 nM in each case). Somatostatin was effective against epinephrine-stimulated, but not basal, TSH secretion (80 +/- 4% inhibition; ED50, 1 +/- 3 nM). The data show that epinephrine is a potential regulator of TSH secretion by its own action and via its interactions with TRH, dopamine, and somatostatin.

Thyrotropin regulates thyrotroph responsiveness to dopamine in vitro.

The effect of conditioned vs. fresh culture medium on the dopaminergic inhibition of TSH and PRL secretion by primary cultures of male rat anterior pituitary cells has been studied. In the presence of conditioned medium (that had been in contact with the cells over the 3-day culture period) 10(-6) M dopamine (DA) inhibited PRL secretion by 50% and TSH secretion by 30%. After 4 h of incubation with fresh medium 10(-6) M DA still inhibited PRL secretion by 50% but increased TSH release by 20%. TSH release was rapid and could be prevented by 10(-6) M prazosin, an alpha 1 adrenoreceptor antagonist. Fresh medium did not alter TRH induced TSH release. In parallel cultures and under identical conditions fresh medium reduced [3H]dihydroergocryptine (DHE) binding to DA receptors from 2.5 +/- 0.4 fmol/10(5) cells to 0.95 +/- 0.3 fmol/10(5) cells (means +/- SEM, n = 5, P less than 0.001). The effect of fresh medium was dose dependent against the dopaminergic inhibition of TSH secretion and against DA receptor binding. If 1 mU TSH was included, in fresh medium, the dopaminergic inhibition of TSH secretion remained unchanged and [3H]DHE binding to DA receptors did not fall. The rank order of potency of thyroid stimulators was bovine TSH (21 U/mg) greater than semipurified bovine TSH (Thytropar, 1.4 U/mg) greater than endogenous rat TSH (0.03 U/mg expressed as NIADDK-rat TSH-RP2) greater than Graves' immunoglobulin G (0.01 U/mg) when either DA or bromocriptine was used as the dopaminergic agonist. When anterior pituitary cells from hypothyroid rats were examined, the effects of culture medium on the dopaminergic inhibition of TSH and on DA receptor binding were approximately twice those observed in normal cells, but the inclusion of 1 mU TSH in the fresh medium completely prevented the loss of DA function and binding. PRL, human CG, ACTH, insulin, glucagon, and heat-inactivated TSH were unable to prevent the effect of medium replacement on dopaminergic inhibition of TSH and DA receptor binding. The data suggest a mechanism whereby TSH may control its own secretion via DA.

Hypothalamic D2 receptors mediate the preferential release of somatostatin-28 in response to dopaminergic stimulation.

We have studied the effect of dopamine (DA) together with agonist and antagonist drugs of varying specificity on the release of immunoreactive forms of somatostatin (SS) from the perfused, adult rat hypothalamus in vitro. Levels of SS increased from 14.7 +/- 3.7 pg (mean +/- SE) under basal conditions to 137 +/- 23.0 pg after exposure to 10(-6) M DA. This dopaminergic effect was mimicked by the specific D2 agonists bromocriptine (10(-7) M) and LY 171555 (10(-6) M) but not by the D1 agonist SKF 38393A (10(-6) M). The stimulatory action of DA (10(-6) M) was blocked by the active (d) but not the inactive (l) isomer of butaclamol (10(-7) M). Similar blockade was achieved with the specific D2 antagonists metoclopramide (10(-8) M) and domperidone (10(-8) M), whereas the D1 antagonist SCH 23390 partially blocked the stimulation of DA but only when used at X100 greater concentration (10(-6) M). SCH 23390 (10(-8) M) did not affect the dopaminergic stimulation of SS release. HPLC characterization of the immunoreactive forms of SS yielded two peaks which corresponded to SS-28 and SS-14. The ratio of these forms varied significantly under different conditions. In the basal state the ratio of SS-28 to SS-14 was 1:4.4; in response to stimulation with DA, the ratio was 1:1.7 and in response to depolarization with 60 mM K+ the ratio was 1:3.1. In conclusion, the stimulatory action of DA on SS release is mediated via hypothalamic D2 receptors. Furthermore dopaminergic stimulation increases the molar ratio of SS-28 to SS-14 in the total immunoreactive SS which is released.

Dopamine receptors on intact anterior pituitary cells in culture: functional association with the inhibition of prolactin and thyrotropin.

Dopamine (DA) and the dopaminergic agonists bromocriptine and apomorphine inhibit the secretion of TSH as well as that of PRL by rat anterior pituitary (AP) cells in monolayer culture. The order of potency of the drugs is the same for the inhibition of both hormones: bromocriptine ED50 = 0.006 nM against PRL and 0.017 nM against TSH; apomorphine ED50 = 2.9 and 4.8 nM, respectively, and DA, ED50 = 30 and 370 nM, respectively. The dopaminergic antagonists domperidone (DOM) and metoclopramide prevent the inhibition of TSH and PRL by 10(-6) M DA (IC50 = 0.012 and 0.32 nM for metoclopramide against PRL and TSH, respectively; similarly, IC50 = 0.01 and 0.61 nM for DOM). The action of butaclamol is shown to be stereospecific, in that the (+) isomer is 1000-fold more potent in reversing the inhibition of both TSH and PRL by 10(-6) M DA than the (-) isomer [IC50 = 1.1 and 7200 nM for the (+) and (-) isomers against PRL; similarly, 6.3 and 2600 nM against TSH]. The use of radioligand-binding techniques with tritiated DOM ([3H]DOM) and dihydroergocriptine ([3H]DHE) has demonstrated a high affinity dopaminergic binding site upon rat AP cells under the same conditions as the cell cultures used in the hormone secretion studies. Both ligands have been shown to label a site with high affinity (Kd = 1-2 nM) and low capacity (2-3 fmol/10(5) cells). At this site, dopaminergic agonists and antagonists compete with both radioligands and display a rank order of potency which is the same as that shown against TSH and PRL secretion and which is typically dopaminergic. For [3H]DHE: bromocriptine Ki (0.04 nM) greater than metoclopramide = DOM (0.07 nM) greater than (+)butaclamol (0.7 nM) greater than apomorphine (20 nM) greater than DA (700 nM) greater than (-)butaclamol (2000 nM). Similar data were derived using [3H]DOM. The high affinity site is saturable, has rapid association and dissociation rates, as determined for both radioligands used, and is temperature dependent. In contrast, both radioligands bind to a second binding site on the cells that is of lower affinity (Kd = 244 nM for [3H]DOM and 678 nM for [3H]DHE) and larger capacity (100 fmol/10(5) cells for both ligands). This second site is neither stereospecific nor, using the methodology presented here, does it discriminate between other dopaminergic compounds. It is thus not considered to represent specific DA receptor binding. It is concluded that the dopaminergic stimulus causing the inhibition of TSH and PRL secretion from rat AP cells in culture is mediated via a high affinity DA receptor present upon lactotrophs and thyrotrophs and that this receptor has similar characteristics on the two cell types.

Release of an active sodium transport inhibitor (ASTI) from rat hypothalamic cells in culture.

To investigate the hypothesis whether the hypothalamus releases an active (ouabain-sensitive) sodium transport inhibitor, we cultured hypothalamic and cortical cells from day 17 fetal rats. Culture media from hypothalamic cells reduced the total erythrocyte sodium efflux rate constant from 0.487 +/- (SE) 0.014 to 0.408 +/- 0.013 (P less than 0.001), and the ouabain-sensitive rate constant from 0.305 +/- 0.015 to 0.240 +/- 0.016 (P less than 0.01). Hypothalamic media also showed a dose-dependent displacement of [3H]-ouabain-binding to erythrocyte membranes. Neither cortical nor conditioned media (incubated without cells) had any effect. Various well-characterized hormones of hypothalamic origin failed to inhibit sodium efflux rate constant. These studies demonstrate that fetal rat hypothalamic cells contain and release a factor which inhibits sodium transport in human erythrocytes.

Adenosine-regulated cell proliferation in pituitary folliculostellate and endocrine cells: differential roles for the A(1) and A(2B) adenosine receptors.

A(1) and A(2) adenosine receptors have been identified in the pituitary gland, but the cell type(s) on which they are located and their effects on pituitary cell growth are not known. Therefore, we analyzed the expression of A(1) and A(2) receptors in primary rat anterior pituitary cells, two pituitary folliculostellate (TtT/GF and Tpit/F1) and two pituitary endocrine (GH(3) and AtT20) cell lines, and compared their effects on cell proliferation. In anterior pituitary and folliculostellate cells, adenosine and adenosine receptor agonists (5'-N-ethylcarboxamidoadenosine, a universal agonist, and CGS 21680, an A(2A) receptor agonist) stimulated cAMP levels with a rank order of potency that indicates the presence of functional A(2B) receptors. This stimulation, however, was not observed in either GH(3) or AtT20 cells, where adenosine and the A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine inhibited VIP/forskolin-stimulated cAMP production. Expression of A(2B) and A(1) receptors in the folliculostellate cells and that of the A(1) receptor in the endocrine cells were confirmed by RT-PCR, immunocytochemistry, and ligand binding. Adenosine and 5'-N-ethylcarboxamidoadenosine dose-dependently (10 nM to 10 microM) stimulated growth in the folliculostellate, but not in the endocrine, cells, whereas in the latter, 100 microM adenosine and 2-chloro-N(6)-cyclopentyladenosine inhibited cell proliferation by slowing cell cycle progression. These data highlight the differential expression of A(1) and A(2B) adenosine receptors in pituitary cells and provide evidence for opposing effects of adenosine on pituitary folliculostellate and endocrine cell growth.

The validity of estimating total body fat and fat-free mass from skinfold thickness in adults with growth hormone deficiency.

The regression equations of Durnin and Womersley for estimating total body fat (TBF) and fat-free mass (FFM) from skinfold thickness were validated for adult GH-deficient (GHD) patients by comparing the values of TBF and FFM from the prediction equations with the directly measured values from dual energy x-ray absorptiometry. Twenty-seven male and 24 female patients (aged 21-61 yr) were studied. GHD was isolated in 5 cases and was part of a spectrum of hypopituitarism due to a variety of causes in 46 cases. The mean period of GHD was 6.9 +/- 4.6 yr. All patients were receiving stable replacement therapy. The validation statistics showed no significant differences (P > 0.05) between measured and predicted values of TBF and FFM in either males (24.5 vs. 24.9 and 65.5 vs. 65.8 kg) or females (24.6 vs. 26.3 and 44.7 vs. 43.9 kg). Mean differences were smaller in males (0.4 and 0.2 kg) than females (1.7 and -0.8 kg); they were less than 1% in males and less than 2% in females. Therefore, the Durnin and Womersley equations are suitable for general use with GHD patients. Using TBF (kilograms) from dual energy x-ray absorptiometry as the dependent variable and the log of the sum of skinfold thickness as the independent variable, linear regression equations were formulated to predict TBF in GHD patients. The lowest SE of estimate was 3.8 kg in males and 4.6 kg in females. To determine their general applicability, these equations will need to be cross-validated.

Early morning hyperglycemia in insulin-dependent diabetes: acute and sustained effects of cholinergic blockade.

Nocturnal release of GH has been shown to be related to the early morning rise in plasma glucose (PG) seen in insulin-dependent diabetes mellitus (IDDM). We have studied the effects of suppression of nocturnal GH release during a single night (acute study) and after nightly suppression for 1 week (chronic study). Changes in plasma glucose and counter-regulatory hormone concentrations were monitored in six IDDM patients during a constant overnight insulin infusion alone, after addition of the anticholinergic agent pirenzepine to cause acute GH suppression, and again on the seventh night of such treatment. In control experiments (infusion of insulin alone; 0.075 mU/kg.min) PG increased from (mean +/- SEM) 5.6 +/- 0.6 mmol/L at 2400 h to 11.1 +/- 1.3 mmol/L at 0900 h (P = 0.0024). Addition of pirenzepine (100 mg at 2200 h and again at 2400 h) in the acute study resulted in a PG change from 5.6 +/- 0.3 mmol/L at 2400 h to 8.4 +/- 1.4 mmol/L at 0900 h (P = 0.17). After pirenzepine administration at the same dose for 7 nights, PG increased from 4.7 +/- 0.6 mmol/L at 2400 h to 6.8 +/- 1.2 mmol/L at 0900 h (P = 0.11). Increases in PG during the study period were significantly less after chronic treatment than after acute treatment compared with changes on control nights. The nocturnal release of GH, which was demonstrated in all patients during the control nights, was suppressed in all patients during the acute study and in four of six patients during the chronic studies. We conclude that initial reduction of the early morning rise of PG in IDDM is associated with acute suppression of nocturnal GH release, and that the more significant sustained effect of anticholinergic GH suppression on the rise of PG may be associated with additional indirect effects on insulin clearance.

Body composition derived from whole body counting of potassium in growth hormone-deficient adults: a possible low intracellular potassium concentration.

The validity of total body potassium (TBK) measurement in estimating fat mass and fat-free mass (FFM) in GHD adults was assessed by comparison with the reference technique of dual energy x-ray absorptiometry (DEXA). The TBK and FFM values determined by DEXA were used to calculate the potassium concentration per kg FFM in GH-deficient (GHD) adults and compared with standard values for normal subjects of 59.6 mmol for females and 66.4 mmol for males. There were considerable differences between predicted and measured TBK values for both males (3972 vs. 3577 mmol; P < 0.001) and females (2526 vs. 2277 mmol; P < 0.001). Similarly, the estimation of FFM and fat mass by TBK measurement was significantly inaccurate for both sexes compared to values determined by DEXA. These discrepancies may be accounted for by the lower calculated potassium concentrations compared with standard values for both males (56.2 vs. 66.4 mmol; P < 0.001) and females (53.1 vs. 59.6 mmol; P < 0.001). These observations suggest that caution should be exercised in the interpretation of TBK in GHD adults, and the reduced potassium concentrations would alleviate inaccuracies in the estimation of body composition. Secondly, the decreased intracellular potassium concentration of GHD adults may account for the decreased muscle strength and ease of fatigueability seen in GHD adults.

Preliminary characterization of growth factors secreted by human pituitary tumors.

To investigate the secretion of mitogenic factors by human pituitary tumors we have cultured cells from 54 adenomas in serum-free medium. Conditioned media from 28 (52%) elicited dose-dependent stimulation of [3H]thymidine incorporation into rat GH3 cells (22-338% above control), while 14 (26%) inhibited GH3 proliferation. Stimulating activity was observed more frequently in nonfunctional tumor-conditioned medium (73%; n = 22) than in secretory tumor-conditioned medium (37%; n = 32). Of 10 tumour-conditioned media with mitogenic activity for GH3 cells, only 4 produced modest stimulation of HEp2 (human laryngeal carcinoma) cells. In contrast, [3H]thymidine incorporation into A431 (human squamous carcinoma) and PC12 (rat adrenal pheochromocytoma) cells was enhanced by each of 15 tumor-conditioned media (up to 342% and 275%, respectively), 8 of which had shown stimulatory and 2 inhibitory effects on GH3 cells. Gel filtration of pooled conditioned media from 10 nonfunctional tumors showed significant growth-promoting activity for GH3 cells in fractions corresponding to mol wt of 2-3 and 11-18 kDa. Proliferative activity on A431 cells also eluted in two positions; one corresponded to the higher mol wt peak seen with GH3 cells, while the other, not observed with GH3 cells, was in the 3- to 6-kDa range. These findings suggest that cells derived from human pituitary adenoma tissue synthesize and secrete several growth factors, each of which may have its own target cell specificities. These factors have yet to be characterized, but we suggest that they may have a role in stimulating the development or maintenance of human pituitary adenomas.