Treatment of pituitary-dependent Cushing's disease with the multireceptor ligand somatostatin analog pasireotide (SOM230): a multicenter, phase II trial.

CONTEXT: There is currently no medical therapy for Cushing's disease that targets the pituitary adenoma. Availability of such a medical therapy would be a valuable therapeutic option for the management of this disorder. OBJECTIVE: Our objective was to evaluate the short-term efficacy of the novel multireceptor ligand somatostatin analog pasireotide in patients with de novo, persistent, or recurrent Cushing's disease. DESIGN: We conducted a phase II, proof-of-concept, open-label, single-arm, 15-d multicenter study. PATIENTS: Thirty-nine patients with either de novo Cushing's disease who were candidates for pituitary surgery or with persistent or recurrent Cushing's disease after surgery without having received prior pituitary irradiation. INTERVENTION: Patients self-administered sc pasireotide 600 microg twice daily for 15 d. MAIN OUTCOME MEASURE: Normalization of urinary free cortisol (UFC) levels after 15 d treatment was the main outcome measure. RESULTS: Of the 29 patients in the primary efficacy analysis, 22 (76%) showed a reduction in UFC levels, of whom five (17%) had normal UFC levels (responders), after 15 d of treatment with pasireotide. Serum cortisol levels and plasma ACTH levels were also reduced. Steady-state plasma concentrations of pasireotide were achieved within 5 d of treatment. Responders appeared to have higher pasireotide exposure than nonresponders. CONCLUSIONS: Pasireotide produced a decrease in UFC levels in 76% of patients with Cushing's disease during the treatment period of 15 d, with direct effects on ACTH release. These results suggest that pasireotide holds promise as an effective medical treatment for this disorder.

Growth hormone: independent release of big and small forms from rat pituitary in vitro.

Sequential release of big and small forms of growth hormone by perifused rat pituitaries has been demonstrated by immunoprecipitation. The results suggest that either the two forms are independently synthesized and released, or that a newly synthesized molecule of big growth hormone follows one of two paths: direct release or intracellular processing through the storage compartment with conversion to small growth hormone.

Hypothalamic stimulation of growth hormone secretion.

Stimulation of the ventromedial hypothalamic nucleus in rats resulted in increased plasma growth hormone levels within 5 minutes, as measured by radioimmunoassay. Stimulation of the cerebral cortex was without effect. These observations confirm previous results involving destructive lesions and establish the ventromedial nucleus as a hypothalamic locus involved in the control of growth hormone secretion.

Somatomedin-C mediates growth hormone negative feedback by effects on both the hypothalamus and the pituitary.

Somatomedin-C stimulates somatostatin release to a maximum of 390 percent of basal release during short-term (20-minute) incubation of rat hypothalamus. It has no effect on basal or stimulated growth hormone release from primary cultures of rat adenohypophyseal cells during a 4-hour incubation, but inhibits stimulated release by more that 90 percent after 24 hours. These findings suggest that somatomedin-C participates in the growth hormone negative feedback loop with an immediate effect on hypothalamic somatostatin and a delayed effect on the anterior pituitary.

Receptor-associated resistance to growth hormone-releasing factor in dwarf "little" mice.

Anterior pituitaries from the dwarf mouse strain "little" did not release growth hormone or accumulate adenosine 3',5'-monophosphate (cyclic AMP) in response to human and rat growth hormone-releasing factor (GRF). Dibutyryl cyclic AMP, as well as the adenylate cyclase stimulators forskolin and cholera toxin, markedly stimulated growth hormone (GH) release. The basis of the GH deficiency in the little mouse may therefore be a defect in an early stage of GRF-stimulated GH release related either to receptor binding or to the function of the hormone-receptor complex.

Cortisol induction of growth hormone synthesis in a clonal line of rat pituitary tumor cells in culture.

Growth hormone synthesis increased markedly after addition of glucocorticoids at physiological concentrations to cultures of the GH(1) line of rat pituitary tumor cells. Stimulation of hormone protein synthesis by corticosteroids was selective, since (i) the rate of hormone synthesis increased while total protein synthesis decreased, and (ii) cortisol analogs, biologically inactive metabolites, and sex steroids did not induce growth hormone synthesis.

Growth hormone-releasing hormone.

The identification of GRH has been followed by an extraordinarily rapid rate of knowledge accumulation. Within a period of slightly more than 3 yr since the structure of the GRH was determined, nearly 500 papers have been published pertaining to the hormone. Extensive knowledge of its anatomy, chemistry, molecular biology, physiology, and pathology has been gathered and, in particular, studies in humans have proceeded faster than with any other of the hypophysiotropic hormones. New insights have been gained with respect to the pathogenesis of both GH deficiency and GH excess states, and the use of GRH and its analogs as diagnostic and therapeutic agents already represents a reality.

Loss of central nervous system component of dopaminergic inhibition of prolactin secretion in patients with prolactin-secreting pituitary tumors.

The administration of l-dopa suppresses prolactin (PRL) secretion in normal subjects and in patients with hyperprolactinemia, although it is not known whether this effect, which requires the conversion of dopa to dopamine, is mediated peripherally or through the central nervous system. To distinguish between these effects, 10 normal subjects (6 male, 4 female) and 8 patients with hyperprolactinemia associated with pituitary tumors were given l-dopa, 0.5 g alone, or 0.1 g after a 24-h pretreatment with carbidopa, 50 mg every 6 h, which produces peripheral dopa decarboxylase inhibition. Similar degrees of PRL suppression were observed in normal subjects (basal plasma PRL 13+/-2 ng/ml) after l-dopa alone (48+/-4%) and after l-dopa plus carbidopa (58+/-6%). In patients with pituitary tumors and elevated plasma PRL (73+/-14 ng/ml), l-dopa alone led to PRL suppression comparable with that in normal subjects (47+/-6%). However, l-dopa plus carbidopa resulted in only minimal suppression of plasma PRL (19+/-4%) which was significantly less than after l-dopa alone (P < 0.001). Urinary homovanillic acid excretion, which reflected peripheral dopa decarboxylation was similar in controls and tumor patients after l-dopa both alone and after carbidopa pretreatment. Comparable suppression of PRL levels in response to a dopamine infusion (4 mug/kg per min for 3 h) was observed in controls and tumor patients. The results indicate that although peripheral conversion of exogenous dopa to dopamine can suppress PRL secretion, in normals, the central nervous system conversion of dopa to dopamine in the presence of peripheral dopa decarboxylase inhibition is sufficient to account for its PRL-suppressive effects. In contrast, patients with tumors, while retaining peripheral dopaminergic inhibitory effects on PRL secretion, exhibit a marked reduction of central dopaminergic inhibition of PRL secretion.

Release of somatostatin-like immunoreactivity from incubated rat hypothalamus and cerebral cortex. Effects of glucose and glucoregulatory hormones.

Somatostatin (SRIF) is localized in the hypothalamus, extrahypothalamic brain, and throughout the gastrointestinal tract. Release of gastrointestinal SRIF-like immunoreactivity (SRIF-LI) is under nutrient regulation but the effect of nutrients on neural SRIF-LI is unknown. The present studies examined the effects of glucose uptake and metabolism and hormones influencing glucose disposition on SRIF-LI release from medial basal hypothalamus (MBH) and cerebral cortex (Cx) incubated in Krebs-Ringer bicarbonate containing bacitracin. After a preincubation to achieve stable secretion, tissues were incubated for 20 min in 14 mM glucose (basal) and then, for 20 min in fresh medium with test materials. MBH SRIF-LI release was inversely related to medium glucose concentration with release in the absence of glucose (235+/-42 pg/MBH per 20 min) more than five times that in the presence of 25 mM glucose (46+/-4 pg/20 min). In the presence of 14 mM glucose MBH SRIF-LI release was stimulated above basal by agents interfering with glucose uptake including 3-O-methyl-d-glucose (42 mM; 70+/-5 vs. 42+/-3 pg/20 min, P < 0.05), phlorizin (50 mM; 351+/-63 vs. 29+/-2 pg/20 min, P < 0.001) or cytochalasin B (20 muM; 110+/-7 vs. 22+/-2 pg/20 min, P < 0.001). Inhibition of glucose metabolism by 2-deoxy-d-glucose resulted in dose-related stimulation of MBH SRIF-LI release (maximal at 28 mM; 201+/-28 pg/20 min vs. 32+/-4 pg/20 min, P < 0.001). Viability of MBH was unimpaired by incubation in the absence of glucose or following exposure to 2-deoxy-d-glucose as determined by retention of SRIF-LI responsiveness to stimulation by potassium (60 mM) or neurotensin (5 muM). In contrast, Cx SRIF-LI release was slightly inhibited by decreases in medium glucose and unaffected by inhibition of glucose uptake or metabolism. These results provide evidence for nutrient regulation of MBH but not Cx SRIF-LI release and may explain inhibition of growth hormone seen in the rat in response to hypoglycemia. Insulin (10 nM-1 muM) stimulated MBH but not Cx SRIF-LI release while glucagon was without effect. Our previous demonstration that MBH SRIF-LI release was stimulated by somatomedin-C, but not insulin at physiologic concentrations, is consistent with an action of insulin through the somatomedin-C receptor at the doses studied. Our studies indicate a regional specificity for the control of SRIF secretion within the brain and suggests the possibility of a role for hypothalamic SRIF in metabolic regulation.

Decreased hypothalamic growth hormone-releasing hormone content and pituitary responsiveness in hypothyroidism.

The effects of thyroidectomy (Tx) and thyroxine replacement (T4Rx) on pituitary growth hormone (GH) secretion and hypothalamic GH-releasing hormone (GRH) concentration were compared to define the mechanism of hypothyroid-associated GH deficiency. Thyroidectomized rats exhibited a complete loss of pulsatile GH secretion with extensive reduction in GRH responsiveness and pituitary GH content. Cultured pituitary cells from Tx rats exhibited reduced GRH sensitivity, maximal GH responsiveness, and intracellular cyclic AMP accumulation to GRH, while somatostatin (SRIF) suppressive effects on GH secretion were increased. Hypothalamic GRH content was also markedly reduced. T4Rx completely restored hypothalamic GRH content and spontaneous GH secretion despite only partial recovery of pituitary GH content, GRH and SRIF sensitivity, and intracellular cyclic AMP response to GRH. The results indicate multiple effects of hypothyroidism on GH secretion and suggest that a critical role of T4 in maintaining normal GH secretion, in addition to restoring GH synthesis, is related to its effect on hypothalamic GRH.

Dipeptidylpeptidase IV and trypsin-like enzymatic degradation of human growth hormone-releasing hormone in plasma.

The plasma enzyme responsible for primary proteolytic cleavage of growth hormone-releasing hormone (GRH) at the 2-3 amino acid bond was characterized. Native GRH[GRH(1-44)-NH2 and GRH(1-40)-OH], and COOH-terminally shortened fragments [GRH(1-32)-NH2 and GRH(1-29)-NH2] were rapidly cleaved, while GRH(2-32)-NH2 was not degraded at this site. Moreover, degradation to GRH(3-44)-NH2 was unaffected by an aminopeptidase inhibitor, indicating that this metabolite was generated from a single step cleavage by a dipeptidylpeptidase (DPP) rather than sequential aminopeptidase cleavages. Conversion to GRH(3-44)-NH2 was blocked by diprotin A, a DPP type IV (DPP IV) competitive inhibitor. D-Amino acid substitution at either position 1 or 2 also prevented hydrolysis, characteristic of DPP IV. Analysis of endogenous plasma GRH immunoreactivity from a human GRH transgenic pig revealed that the major peak coeluted with GRH(3-44)-NH2. Native GRH exhibited trypsin-like degradation at the 11-12 position but cleavage at the 12-13 site occurred only with GRH(1-32)-NH2 and GRH(1-29)-NH2. Formation of these metabolites was independent of prior DPP IV hydrolysis but was greatly reduced by trypsin inhibitors. Evaluation of plasma stability of potential GRH super analogues, designed to resist degradation by these enzymes, confirmed that GRH degradation in plasma occurs primarily by DPP IV, and to a lesser extent by trypsin-like enzyme(s).

Measurement of growth hormone-releasing hormone and somatostatin in hypothalamic-portal plasma of unanesthetized sheep. Spontaneous secretion and response to insulin-induced hypoglycemia.

To elucidate the role of growth hormone (GH)-releasing hormone (GRH) and somatostatin (SRIH) in the regulation of the growth hormone (GH) secretory pattern, we collected portal blood from five unanesthetized ovariectomized ewes for repeated measurements of GRH and SRIH simultaneous with those of peripheral GH. Hormones were measured at 10-min intervals for 5.5 h and their interrelationships analyzed. Mean portal GRH was 20.4 +/- 6.7 (SD) pg/ml and the estimated overall secretion rate was 13 pg/min. GRH secretion was pulsatile with peaks of 25-40 pg/ml and a mean pulse interval of 71 min. Mean portal SRIH was 72 +/- 33 pg/ml and the estimated overall secretion rate was 32 pg/min. SRIH secretion was also pulsatile with peaks of 65-160 pg/ml and a mean pulse interval of 54 min. The GH pulse interval was 62 min. A significant association was present between GRH and GH secretory peaks though not between GRH and SRIH or SRIH and GH. Insulin hypoglycemia resulted in a rapid and brief stimulation of SRIH secretion followed by a decline in GH levels. No effect was observed on GRH secretion until 90 min, when a slight increase occurred. The results suggest (a) the presence of an independent neural rhythmicity of GRH and SRIH secretion with a primary role of GRH in determining pulsatile GRH secretion, and (b) that the inhibitory effects of insulin hypoglycemia on GH in this species are attributable to a combination of enhanced SRIH secretion and possibly other factors, though without significant inhibition of GRH.

Partial purification and characterization of a peptide with growth hormone-releasing activity from extrapituitary tumors in patients with acromegaly.

Growth hormone (GH)-releasing activity has been detected in extracts of carcinoid and pancreatic islet tumors from three patients with GH-secreting pituitary tumors and acromegaly. Bioactivity was demonstrated in 2 N acetic acid extracts of the tumors using dispersed rat adenohypophyseal cells in primary monolayer culture and a rat anterior pituitary perifusion system. The GH-releasing effect was dose responsive and the greatest activity was present in the pancreatic islet tumor. Small amounts of activity were also found in two other tumors (carcinoid and small cell carcinoma of lung) unassociated with GH hypersecretion. Each of the tumors contained somatostatin-like immunoreactivity but the levels did not correlate with the net biologic expression of the tumor. Sephadex G-75 gel filtration indicated the GH-releasing activity to have an apparent molecular size of slightly greater than 6,000 daltons. The GH-releasing activity was adsorbed onto DEAE-cellulose at neutral pH and low ionic strength, from which it could be eluted by increasing ionic strength. The GH-releasing activity was further purified by high pressure liquid chromatography using an acetonitrile gradient on a cyanopropyl column to yield a preparation that was active at 40 ng protein/ml. Partially purified GH-releasing activity, from which most of the bioactive somatostatin had been removed, increased GH release by pituitary monolayer cultures to five times base line. Enzymatic hydrolysis studies revealed that the GH-releasing activity was resistant to carboxypeptidase, leucine-aminopeptidase, and pyroglutamate-amino-peptidase but was destroyed by trypsin and chymotrypsin, indicating that internal lysine and/or arginine and aromatic amino acid residues are required for biologic activity and that the NH2-terminus and CO9H-terminus are either blocked or not essential. The results provide an explanation for the presence of GH-secreting tumors in some patients with the multiple endocrine neoplasia syndrome, type I, and warrant the addition of GH-releasing activity to the growing list of hormones secreted by tumors of amine precursor uptake and decarboxylation cell types.

Growth hormone enhances hepatic epidermal growth factor receptor concentration in mice.

The effect of growth hormone (GH) on binding of epidermal growth factor (EGF) to liver membrane preparations was investigated in hypophysectomized mice and partially GH-deficient, genetic mutant "little" (lit/lit) mice. The EGF binding of normal male mice and testosterone-treated females was higher than in normal females. Due to diminished receptor concentration, hepatic EGF binding was decreased in male and female lit/lit mice to a level that was unaffected by gender or androgen treatment. GH replacement therapy by intermittent injections and continuous infusion restored the EGF binding of hypophysectomized mice to normal male and female levels, respectively, suggesting a role for the more pulsatile GH secretion in normal males. In lit/lit mice, however, both continuous and intermittent GH resulted in EGF binding levels comparable to those in normal females. In normal males continuous GH suppressed EGF binding. In conclusion, endogenous GH secretion induces EGF receptors in mice and this effect may be modulated by sex differences in GH secretion.

Rapid enzymatic degradation of growth hormone-releasing hormone by plasma in vitro and in vivo to a biologically inactive product cleaved at the NH2 terminus.

The effect of plasma on degradation of human growth hormone-releasing hormone (GRH) was examined in vitro and in vivo using high performance liquid chromatography (HPLC), radioimmunoassay (RIA), and bioassay. When GRH(1-44)-NH2 was incubated with human plasma, the t1/2 of total GRH immunoreactivity was 63 min (RIA). However, HPLC revealed a more rapid disappearance (t1/2, 17 min) of GRH(1-44)-NH2 that was associated with the appearance of a less hydrophobic but relatively stable peptide that was fully immunoreactive. Sequence analysis indicated its structure to be GRH(3-44)-NH2. Identity was also confirmed by co-elution of purified and synthetic peptides on HPLC. Biologic activity of GRH(3-44)-NH2 was less than 10(-3) that of GRH(1-44)-NH2. After intravenous injection of GRH(1-44)-NH2 in normal subjects, a plasma immunoreactive peak with HPLC retention comparable to GRH(3-44)-NH2 was detected within 1 min and the t1/2 of GRH(1-44)-NH2 (HPLC) was 6.8 min. The results provide evidence for GRH inactivation by a plasma dipeptidylaminopeptidase that could limit its effect on the pituitary.

Metabolic clearance and plasma disappearance rates of human pancreatic tumor growth hormone releasing factor in man.

The metabolic clearance rate (MCR) and plasma disappearance rate (t1/2) of human pancreatic tumor growth hormone releasing factor [hpGRF(1-40)] was determined in normal adult male subjects by single injection and constant infusion techniques. Single injections of 1, 3.3, and 10 micrograms/kg hpGRF(1-40) were administered intravenously, plasma immunoreactive (IR) GRF levels were measured during the subsequent 180 min, and biexponential curve analysis was performed. Graded, dose-constant infusions of hpGRF(1-40) at rates of 1, 3.3, 10, and 33 ng/kg per min were administered and the MCR was calculated from measurement of steady state plasma IR-GRF levels at each infusion rate. The postinfusion disappearance rate was determined by linear regression analysis of plasma IR-GRF levels during the 120-min period after cessation of the infusion. The calculated MCR during the single injection study was 194 +/- 17.5 liters/m2 per d and was not significantly different from the calculated value during the constant infusion study (202 +/- 16 liters/m2 per d). The disappearance rate during the single injection study was subdivided into two linear phases: an initial equilibration phase (7.6 +/- 1.2 min) and a subsequent elimination phase (51.8 +/- 5.4 min). The latter was similar to the linear disappearance rate observed (41.3 +/- 3.0 min) after cessation of the constant infusion. The chromatographic and biologic characteristics of plasma IR-GRF, 30 min after injection, were similar to those of synthetic hpGRF(1-40). The results have been discussed in relation to the MCR of other hypothalamic hormones and have been used to extrapolate secretion rates of GRF in patients with ectopic GRF production.

Plasma growth hormone responses to constant infusions of human pancreatic growth hormone releasing factor. Intermittent secretion or response attenuation.

Administration of human pancreatic tumor growth hormone (GH) releasing factor (hpGRF[1-40]) as a single injection to normal human subjects stimulates the secretion of GH in a dose-responsive manner. In the present studies, hpGRF(1-40) was infused in a graded stepwise manner over a 6-h period in order to determine whether the GH secretory response would be sustained. Normal adult males received four consecutive 90-min infusions of hpGRF(1-40) at doses of 1, 3.3, 10, and 33 ng/kg per min, preceded and followed by a 90-min saline infusion; and the plasma GH responses were compared with those during a separate control infusion. Plasma GH levels were significantly elevated by each hpGRF(1-40) infusion; and dose responsiveness was evident for the lowest three doses. Mean integrated GH secretory rates for the four doses were 1.95, 3.29, 4.29, and 3.65 times those of the respective control study. Plasma GH responses exhibited considerable variability, frequently decreasing during the latter part of each infusion; and at the highest dose, they decreased continuously beginning shortly after the onset of infusion. Episodic GH secretion occurred in individual subjects during each of the infusion periods. The possible contribution of hypothalamic somatostatin secretion to the diminished GH responsiveness was evaluated by determining plasma thyroid stimulating hormone (TSH) levels during the infusions and the TSH responses to thyrotropin-releasing hormone (500 micrograms i.v.) during a separate hpGRF(1-40) infusion of 2 ng/kg per min. Neither basal nor stimulated TSH levels differed between GRF-infused and control groups. The results indicate that GH secretion is dose responsive to hpGRF(1-40) infusions, though the response to hpGRF(1-40) infusions, though the response is complex. The absence of impaired TSH secretion provides evidence against a mediating role of somatostatin. The explanation for the loss of GH responsiveness remains undetermined but could include GRF-induced receptor down-regulation, a postreceptor effect, or, in spite of our negative results, a somatostatin-mediated inhibition.

p27Kip1-deficient mice exhibit accelerated growth hormone-releasing hormone (GHRH)-induced somatotrope proliferation and adenoma formation.

p27Kip1 (p27) controls cell cycle progression by binding to and inhibiting the activity of cyclin dependent kinases. Disruption of the p27 gene in mice (p27-/-) results in increased body growth with a disproportionate enlargement of the spleen, thymus, testis, ovary and pituitary. The increase in pituitary size is due to selective hyperplasia of the intermediate lobe (IL) while the anterior lobe (AL) is not overtly affected. p27 heterozygous mice (p27+/-), as well as p27-/- mice, are hypersensitive to radiation- and chemical-induced tumors compared to wildtype (p27+/+) littermates. Therefore, unlike classical tumor suppressors, only a reduction in p27 levels is necessary to predispose tissues to secondary tumor promoters. Consistent with these studies is the fact that the p27 gene sequence and mRNA levels appear normal in human pituitary adenomas while p27 protein levels are decreased. Therefore, a reduction in p27 levels could be sufficient to sensitize pituitary cells to tumorigenic factors. To test this hypothesis, metallothionein promoter-driven, human growth hormone-releasing hormone (MT-hGHRH) transgenic mice, that exhibit somatotrope hyperplasia before 9 months of age and subsequent adenoma formation with 30 - 40% penetrance, were crossbred with p27+/- mice for two successive generations to produce p27+/+, p27+/- and p27-/- mice that expressed the hGHRH transgene. At 10 - 12 weeks of age, p27-/- and p27+/+, hGHRH mice were larger than their p27+/+ littermates and displayed characteristic hyperplasia of the IL and AL, respectively. Expression of the hGHRH transgene in both p27+/- and p27-/- mice selectively expanded the population of somatotropes within the AL, where pituitaries of p27+/-, hGHRH and p27-/-, hGHRH mice were two- and fivefold larger than p27+/+, hGHRH pituitaries, respectively. There was also a synergistic effect of hGHRH transgene expression and p27-deficiency on liver, spleen and ovarian growth. At 6 - 8 months of age, 83% of p27+/-, hGHRH mice displayed macroscopic AL adenomas (>100 mg), while all pituitaries from p27+/+, hGHRH mice remained hyperplastic (<20 mg). In contrast to the dramatic effects of p27-deficiency on hGHRH-induced organ growth, elimination of p53, by crossbreeding MT-hGHRH mice to p53-deficient mice, did not augment the hyperplastic/tumorigenic effects of hGHRH transgene expression. Taken together these results demonstrate that a reduction in p27 expression is sufficient to sensitize somatotropes to the proliferative actions of excess GHRH, resulting in the earlier appearance and increased penetrance of hGHRH-induced pituitary tumors.

Possible evidence for the existence of a growth hormone fragment in porcine pituitary.

In an attempt to search for growth hormone fragments in the pituitary, a radioimmunoassay was developed for a 55 residue S-amino-ethylated CNBr fragment (fragment B) of porcine growth hormone corresponding to residues 126-180 of human growth hormone. The assay was sensitive to 50 pg of fragment B whereas displacement of 125I-labelled fragment B by procine growth hormone required a 10(3) M excess and was non-parallel. In a homogolous porcine growth hormone radioimmunoassay, fragment B was non-reactive. Gel filtration of an extract of porcine pituitary on Sephadex G-75 revealed three peaks of fragment B immunoreactivity: peak I (29% of total immunoreactivity) eluted in the void volume, peak II (49%) eluted in the position of growth hormone, and peak III (12%) was more retarded than fragment B. Nearly all of the growth hormone immunoreactivity eluted as a single peak in the position of 125I-labelled porcine growth hormone. The dilution curve of peak III but not of peaks I or II was parallel to that of fragment B. The results indicate the existence within porcine pituitary of material cross-reactive with a portion of the growth hormone molecule, possible representing a growth hormone fragment.

Neurotensin hyperglycemia:evidence for histamine mediation and the assessment of a possible physiologic role.

The hyperglycemic and hyperglucagonemic effects of systemically administered neurotensin in rats were investigated to explore the possibility that they are mediated by histamine and to determine whether neurotensin might have a role in the mediation of the responses to central nervous system glucopenia. The hyperglycemic response to neurotensin was partially blocked by the histamine H-1 receptor blockers, diphenhydramine and promethazine, and by the H-2 receptor blocker, cimetidine. The hyperglucagonemic response was completely blocked by diphenhydramine and promethazine and only partially blocked by cimetidine. The effects of histamine on glucose, glucagon, and insulin secretion were similar to those of neurotensin, and the inhibitory effects of both H-1 and H-2 blockers were comparable. The stimulatory effect of histamine on insulin secretion observed after adrenal autotransplantation was also similar to that previously reported for neurotensin. Neither antineurotensin serum nor diphenhydramine, however, was effective in blocking the hyperglycemic and hyperglucagonemic responses to the central administration of 2-deoxyglucose. The results are consistent with a histamine mediation of the effects of exogenously administered neurotensin but do not support a proposed role for neurotensin or histamine in the mediation of the hyperglycemic and hyperglucagonemic responses to central glucopenia.