Fasting associated with decrease in hypothalamic beta-endorphin.

In rats that were fasted for 2 to 3 days there was a decline in hypothalamic, but not pituitary, beta-endorphin. There was no change in pituitary or hypothalamic adrenocorticotropin content as a result of fasting. Endogenous opiates may be involved in physiological adaptation to fasting.

Effect of glucose on the growth hormone response to L-dopa in normal and diabetic subjects.

The effect of hyperglycemia on the growth hormone response to oral L-dopa (500 mg.) was assessed in eight normal and eight insulin-dependent diabetic subjects. A peak growth hormone response of 21.0 +/- 4.0 ng./ml. (mean +/- S.E.M.), significantly above baseline (p less than 0.01), was achieved in the normal group following oral L-dopa. Glucose concentrations did not change and were approximately 80 mg./100 ml. throughout. Administration of 100 gm. oral glucose with the L-dopa, or thirty minutes thereafter, totally suppressed the growth hormone response in all eight and six of the subjects, respectively. A peak growth hormone response of 20.0 "/- 1.7 ng./ml. (mean +/- S.E.M.), significantly above baseline (p less than 0.001), was obtained in eight nonobese, insulin-dependent diabetics, in spite of prevailing hyperglycemia (mean plasma glucose 243-258 mg./100 ml.) throughout the test. Endogenous hyperglycemia was achieved in these patients by lessening the usual strict adherence to plasma glucose control for the purpose of the study. These results suggest an abnormality in the hypothalamus or pituitary of diabetic subjects allowing growth hormone responsiveness in spite of hyperglycemia.

Hypothalamic hypopituitarism after pituitary apoplexy in acromegaly.

Pituitary apoplexy in acromegaly is an uncommon event having been recorded approximately 30 times in the English literature. This report records two additional cases that included growth hormone measurements and an assessment of pituitary function. The apoplectic event developed spontaneously in one, and in the other it developed within two weeks of completing a course of radiotherapy to the pituitary gland. Autocure of the acromegaly was apparent. Basal levels of growth hormone were in the normal range but failed to change with provocative stimuli. Luteinizing hormone and follicle-stimulating hormone titers, although detectable, were inappropriately low for the degree of hypogonadism. Pituitary insufficiency was associated with a significant thyroid-stimulating hormone response to protirelin in one patient tested. It is suggested that these experiments of nature lend credence to the proposal that the hypothalamus may play a critical role in the perpetuation of growth hormone hypersecretion in some patients with acromegaly.

Interaction of age and thyroid hormone status on Na+-K+ ATPase in rat renal cortex and liver.

Na+-K+ ATPase was measured in euthyroid, hypothyroid, and hyperthyroid rats aged 6 weeks, 6 months, and 20-24 months. There was a small but significant decline in basal enzyme activity with increasing age in renal cortical tissue. Enzyme activity decreased with hypothyroidism and increased with hyperthyroidism. With increasing age, both the magnitude of the increase resulting from thyrotoxicosis and the absolute enzyme level were significantly less with each increase in the age of the experimental animals. Hypothyroid animals displayed no age-related decline in renal cortical Na+-K+ ATPase. The decline in Na+-K+ ATPase in renal cortical tissue is thyroid hormone dependent. In addition, age modifies the response of Na+-K+ ATPase to thyroid hormone.

Vasoactive intestinal polypeptide is synthesized in anterior pituitary tissue.

Previous studies have suggested that vasoactive intestinal polypeptide (VIP) is involved in regulation of PRL secretion within the pituitary gland. In order to determine whether VIP is synthesized in anterior pituitary tissue, we performed three experiments. In all experiments, anterior pituitaries were obtained from male rats. The tissue was then labeled by incubation in leucine-free minimum essential medium containing [3H]leucine, 14 microCi/ml. In Exp I, the labeled tissue was homogenized, centrifuged, and the supernatant was chromatographed on Sephadex G-50F. The fractions indicated a large peak of counts near the void volume and another peak coeluting with VIP. These latter fractions were pooled and subjected to reverse phase HPLC. Fractions from the HPLC indicated: a protein peak, VIP immunoreactivity, and maximum counts immunoprecipitated by anti-VIP serum at the retention time of synthetic porcine VIP. Exp II consisted of perifusion of labeled pituitary quarters over a 120-min period followed by an additional 60 min in the presence of 56 mM KCl. During this latter period of KCl depolarization, a large amount of 3H-labeled material was secreted. These fractions were then chromatographed on Sephadex G-50F, and the fractions coeluting with [125I]porcine VIP were subjected to immunoprecipitation with anti-VIP serum. In addition, all fractions from the Sephadex column were assayed for VIP, and the only activity was at the elution volume of [125I]porcine VIP. In Exp III, the pituitary labeling procedure included 3.6 X 10(-5) M cycloheximide. Subsequently, the tissue was perifused and the perifusate collected during the 60-min 56 mM KCl perifusion phase was pooled and immunoprecipitated with anti-VIP serum. No immunoprecipitable counts were obtained. These experiments indicate that anterior pituitary tissue synthesizes VIP on the basis of the HPLC profile and immunoprecipitation with specific anti-VIP antiserum. These results, in addition to other studies by our laboratory and others, suggest that intrapituitary VIP may be an important regulator of anterior pituitary hormone secretion, particularly PRL.

The effect of hypoglycemia on hypothalamic thyrotropin-releasing hormone (HRH) in the rat.

A rapid radioimmunoassay for TRH with a high degree of specificity and sensitivity is described. The procedure is capable of measuring TRH in amounts less than 15 pg/tube. Such an assay system has enabled us to study the effect of hypoglycemia on hypothalamic TRH content. Forty-eight female, adult Holtzman rats were divided into 8 groups of 6. Regular insulin was injected intraperitoneally into each rat except for the basal group. A separate batch of similar rats was studied in the same fashion except that saline was injected instead of insulin. Each group of rats was decapitated and the trunk blood collected at 0, 15, 30, 45, 60, 90, 120 and 180 min post-injection. Appropriate tissues were rapidly taken and immediately extracted in ice-cold methanol. Hypothalamic TRH, pituitary TSH, serum TSH and serum triiodothyronine (T3) and thyroxine (T4) were serially determined. In the insulin-treated group, a rapid fall in blood sugar was observed reaching a nadir in 15 min. Hypothalamic TRH fell from a basal mean +/- SE value of 3.25 +/- 0.31 ng to 1.54 +/- 0.14 ng/hypothalamus (P less than 0.01). Pituitary TSH decreased from 10.0 +/- 0.9 mug to a low of 2.6 +/- 0,8 mug/pituitary (P less than 0.02) at 30 min postinsulin. Serum TSH increased from a basal level of 42.5 +/- 20.5 muU/mo to a peak of 102.1 +/- 10.0 muU/ml 45 min (P less than 0.05) after insulin administration. The incremental change in serum T3 occurred at 90 min when T3 levels increased from a baseline of 107.5 +/- 53.7 ng/100 ml to a peak of 711.7 +/- 20.2 ng/100 ml (P less than 0.01). No changes in T4 were observed. The control group of rats did not show significant changes in hypothalamic TRH. The results of the study indicate that hypoglycemia can induce depletion (presumably release) of hypothalamic TRH with a consequent cascade stimulation of the pituitary-thyroid axis.

Vasoactive intestinal polypeptide and thyrotropin-releasing hormone stimulate newly synthesized, not stored, prolactin.

Experiments were designed to determine whether vasoactive intestinal polypeptide (VIP), reported to stimulate basal PRL secretion, affects PRL processing by lactotrophs. Initially, rat anterior pituitary quarters were incubated for 2 h with [3H]leucine, with and without 10(-5) M VIP, and immunoreactive and immunoprecipitable rPRL were measured during 56 mM KCl perifusion to determine total and 3H-labeled PRL, respectively. Inclusion of VIP increased immunoreactive PRL (P less than 0.05), decreased immunoprecipitable PRL (P less than 0.01), and, therefore, decreased the specific activity of labeled PRL (P less than 0.001). These results suggested an enhanced release of newly synthesized PRL before KCl depolarization, thus decreasing the release of labeled PRL. To discriminate between the two PRL pools, newly synthesized and storage, pituitary quarters were incubated with and without 10(-5) M VIP for 4 h with [14C]leucine, 2 h in cold medium and 2 h with [3H]leucine. Immunoprecipitable PRL was measured during perifusion with 56 mM KCl. Data were depicted as the 3H/14C disintegrations per min ratio of PRL released/3H/14C disintegrations per min of total tissue to account for any differences in tissue labeling. This ratio was greater for tissue labeled in the presence of VIP (P less than 0.002). To determine whether VIP, as a secretagogue, differentiates between the newly synthesized and storage pools, VIP was added after pulse chase, as previously described. No preferential release was observed between the two groups. Finally, using the same [3H]- and [14C]leucine-labeling protocol with and without 10(-5) M VIP, tissue was perifused with medium 199 for 1 h, with 10(-5) M TRH for 30 min, with medium 199 for 30 min, and with 56 mM KCl for 1 h. Inclusion of VIP increased the 3H/14C released/3H/14C total tissue ratio during basal perifusion (P less than 0.04) and TRH exposure (P less than 0.05). Within the control group, the TRH ratio was greater than basal (P less than 0.003). These experiments suggest that newly synthesized PRL is preferentially secreted over stored PRL from tissue incubated with VIP during pulse-chase labeling; however, addition of VIP as a secretagogue did not affect either PRL pool preferentially.

Plasma free tryptophan, brain serotonin, and an endocrine profile of the genetically obese hyperglycemic mouse at 4--5 months of age.

Genetically obese hyperglycemic mice (ob/ob) were compared with their nonlittermate lean controls at 4-5 months of age with regard to brain serotonin, pituitary ACTH content, and circulating levels of glucose, glucagon, insulin, TSH, T3, T4, total tryptophan and free tryptophan. Brain serotonin pituitary ACTH content, and plasma insulin, glucose, total tryptophan, and free tryptophan were all significantly higher in obese mice than in the controls. TSH, T3, and T4 were not significantly different in obese mice vs. controls, suggesting that the obese mouse is euthyroid. Fasting improved but failed to normalize the glucose and insulin levels or insulin to glucagon ratios. Since serotonin is an important neurotransmitter with regard to hypothalamic-pituitary function and since its levels in the brain are dependent on the availability of tryptophan, the findings of elevated levels of free tryptophan in the plasma and serotonin in the brain of the obese hyperglycemic mouse may help to explain some of the previously observed abnormalities of pituitary hormone secretion in these animals.

A longitudinal hormonal profile of the genetically obese mouse.

Obese mice (C57BL/6J ob/ob) and their lean littermates were studied at various ages from immediately post weaning until 62 weeks of age, at which mortality increased markedly. Several age-related changes were noted. 1) Plasma glucose levels were elevated in obese mice 5-20 weeks and 62 weeks of age, but were similar to those in the lean mice at 20-60 weeks of age. Plasma insulin levels were elevated in obese mice, and there were no age-related differences. 2) Brain serotonin was elevated in obese mice at all ages and increased with age in both obese and lean animals. 3) Pituitary contents of ACTH and beta-endorphin were elevated in young obese mice and increased further as these mice approached their life expectancy. 4) The ratios of ACTH to beta-endorphin immunoreactivities were similar in obese and lean mice, except in obese mice over 50 weeks of age where this ratio was increased. We conclude that: 1) the obese mouse is characterized by hyperinsulinemia and hyperadrenocorticism throughout its life; 2) the insulin resistance of the obese mouse improves at 20 weeks of age, yet deteriorates as its life expectancy is approached; 3) the obese mouse has an elevated brain serotonin content similar to previously described elevations of the putative neurotransmitters dopamine and norepinephrine in these mice; and 4) as the obese mouse approaches its life expectancy, abnormalities may occur in the synthesis, processing, or secretion of ACTH and/or beta-endorphine.

The effect of acute hypercalcemia on growth hormone release in man.

The growth hormone response to acute hypercalcemia was studied in 9 normal subjects. Growth hormone, calcium, glucose, phosphate and magnesium levels were determined at 30-min intervals during 4-h infusions. Infusions, performed in random order in the subjects, consisted of either normal saline at 3 ml/min for / h or 15 mg calcium/kg (calcium gluconate at 3 ml/min for 3 h followed by normal saline for the fourth hour. Significant hypercalcemia (P less than 0.05) was achieved within 60 min and maintained throughout the infusion. No change in calcium concentrations occurred during normal saline infusions, and phosphate, glucose and magnesium were unchanges in all studies. Growth hormone levels were significantly higher (P less than 0.05) at 60 min and all subsequent determinations during calcium infusion when compared to normal saline infusions. In 6 of the subjects, standard l-dopa provocative testing with an oral dose of 500 mg was preformed during normal saline and calcium infusions identical to those described above. Peak growth hormone responses did not differ significantly following l-dopa during saline or calcium infusion. These results suggest that an acute increase in circulating calcium promotes greater basal growth hormone secretion without a synergistic increase in hypothalamic mediated growth hormone release by l-dopa.

Plasma prolactin-releasing factor-like activity in the amenorrhea-galactorrhea syndrome.

An in vitro bioassay for plasma PRL-releasing factor-like activity has been developed. The method is a three-phase methanol extraction of plasma with extracts of 1.0 ml plasma adjusted to a final volume of 50 microliter. Single 50-microliter aliquots of extract were incubated in 1.0 ml Krebs-Ringer phosphate (KRP) buffer with one rat hemipituitary after a 1-h preincubation. Samples were obtained basally and 30 min after addition of the extract. During each set of incubations, a parallel series of hemipituitaries was incubated in KRP alone. The total nanograms of rat PRL released per mg pituitary tissue during the initial 30 min after preincubation was calculated for all studies. The mean quantity released in KRP alone was considered basal and was subtracted from values obtained during incubation with plasma extracts. The quantity remaining was considered PRL-releasing activity (PRA) of plasma, expressed as nanograms of rat PRL released per mg pituitary. The PRA in plasma from 13 patients with the amenorrhea-galactorrhea syndrome was 132 +/- 17 ng/mg pituitary (X +/- SE), which was significantly greater (P less than 0.001) than the PRA in plasma from eight matched controls [31 +/- 10 ng/mg pituitary (X +/- SE)]. The patients' individual PRL levels were elevated (range, 48-248 ng/ml), and when compared to the PRA in the samples, a highly significant (P less than 0.001) positive correlation evolved. These results indicate that a circulating PRL-releasing factor-like material present in normal plasma is higher in plasma from hyperprolactinemic patients in direct relationship to the PRL concentration. It is possible that this material is related to the pathogenesis of PRL-secreting pituitary disorders.

Chronic propranolol administration impairs glucagon release during insulin-induced hypoglycemia in normal man.

Failure of a plasma glucagon rise in response to insulin-induced hypoglycemia was demonstrated in normal subjects taking therapeutic doses of the nonselective beta-adrenergic blocker, propranolol, for 7 days before testing. This is the first study to examine glucose homeostasis in normal subjects exposed to chronic propranolol therapy and helps to explain the development of spontaneous hypoglycemia in patients, either diabetic or nondiabetic, during beta-adrenergic receptor blockade. Previous studies of the acute parenteral effects of propranolol administration failed to show any significant effect on glucagon secretory dynamics in response to insulin-induced hypoglycemia. In the present study, however, chronic oral administration of propranolol resulted in severe impairment of the expected glucagon rise in response to hypoglycemia and was associated with severe hypoglycemia in one normal subject.

The effect of hypoglycemia on TSH release in man.

The effect of insulin-induced hypoglycemia on TSH release was studied in 7 normal subjects (Group I), 5 patients with sellar enlargment, 1 patient with idiopathic panhypopituitarism (Group II-A) and 2 acromegalic patients (Group II-B). Serial measurements of TSH, GH and corrtisol, after a bolus of insulin (0.1 U/kg body weight), were made over a period of 120 min. The peak TSH value of 8.3 plus or minus 0.9 pU/ml (mean plus or minus SEM) did not differ statistically from the basal value of 6.0 plus or minus 1.3 pU/ml in Group I. GH levels, however, increased from 1.0 plus or minus 0.0 ng/ml to 28.1 plus or minus 4.3 ng/ml, which was highly significant (P less than 0.001). In contrast, Group II-A patients had an increase in serum TSH from 4.3 plus or minus 1.4 pU/ml to 28.6 plus or minus5.7 pU/ml (P less than 0.02). The peak GH levels of 4.0 plus or minus 1.7 ng/ml did not differ significantly from the basal value of 1.2 plus or minus ng/ml. In group II-B, the untreated acromegalic patient (G) did not show alterations in TSH levels consonant with the increase in GH from a basal value of 34.9 ng/ml to a peak of 46.9 ng/ml with the induction of hypoglycemia. In the treated acromegalic subject (H), basal GH increased from 7.8 ng/ml to 11.4 ng/ml with no significant changes in TSH. Serum cortisol levels in Groups I, II-A and II-B did not show consistent inverse relationship to circulating TSH. The observations in this study suggest that hypoglycemia may stimulate TSH release in certain pituitary disorders. Through GH release might play an inhibitory role on TSH secretion, the results suggest other unidentified factor(s).

The interrelationships among prolactin, 1,25-dihydroxyvitamin D, and parathyroid hormone in humans.

Serum PRL, parathyroid hormone (PTH), and plasma 1,25-dihydroxyvitamin D [1,25(OH)2D]concentrations were measured in 6 women and 2 men with hyperprolactinemia, 6 normal men and 7 normal women, 4 men and 4 women with primary hyperparathyroidism, and 16 men and 4 women with Ca nephrolithiasis. Plasma 1,25(OH)2D and serum parathyroid hormone (PTH) concentrations were normal in the women and men with hyperprolactinemia. In patients with primary hyperparathyroidism and elevated serum PTH, plasma 1,25(OH)2D concentrations were elevated but serum PRL levels were normal. Likewise, serum PRL levels were normal in patients with Ca nephrolithiasis who had significantly elevated plasma, 1,25(OH)2D concentrations and normal serum PTH concentrations. Thus, hyperprolactinemia due to pituitary adenoma or idiopathic hypersecretion is not accompanied but elevated plasma concentrations of 1,25(OH)2D.

Correlation of hyperprolactinemia with altered plasma insulin and glucagon: similarity to effects of late human pregnancy.

Plasma glucose and insulin concentrations were measured during oral glucose and iv tolbutamide tolerance tests in nine women with hyperprolactinemia and the amenorrheagalactorrhea syndrome (AGS). Glucose tolerance curves, basal insulin levels, and postchallenge plasma insulin responses were significantly higher in AGS women compared to those in an age- and weight-matched control group. Fasting plasma glucagon concentrations were unaltered in AGS, but suppression of the hormone after oral glucose was greater and more prolonged relative to the control response. Oral glucose tolerance tests were performed on nine normal women during late pregnancy who had physiological hyperprolactinemia comparable to that in the AGS group. Glucose tolerance curves, exaggerated plasma insulin responses, and glucagon suppression resembled those observed in the AGS women. These results suggest that elevated plasma PRL concentrations may contribute to the development of hyperinsulinemia and accentuated glucagon suppression in response to glucose that is characteristic of late human pregnancy.

Hormonal, metabolic and morphologic studies of aged C57BL/6J obese mice.

Genetically obese mice (C57BL/6J-ob/ob), fed ad libitum, demonstrated a precipitous increase in the spontaneous death rate after 50 weeks. The first signs of morbidity were a ruffled hair coat and a progressive motor ataxia. Necropsy revealed that obese mice had pale and fatty livers, urolithiasis and grossly distended bladders. Microscopically, the hepatocellular changes observed in all aged obese mice included: a loss of orientation of hepatocytes, an enormous variability in the size of both hepatocytes and their nuclei, and an extensive deposition of both large and small lipid droplets, confirmed by an increase content of triacylglycerols. A subacute-to-chronic, multifocal, necrotizing hepatitis was also present. Kidneys from aged obese mice contained hypertrophied glomeruli and increased PAS-stained material. Tubular dilation with compaction of the tubular cells was also seen. There were no significant alterations in the microanatomy or mineralization of femurs from obese mice, yet there was a significant increase in plasma alkaline phosphatase activity. In obese mice at 62-63 weeks of age, hyperglycemia was present even in spite of hyperinsulinemia. Pituitary immunoreactive ACTH and its molar ratio to pituitary immunoreactive beta-endorphin were also increased in obese mice at this age. Even though the etiology of the decreased lifespan of genetically obese mice remains uncertain, the possibility is discussed that an overall defect in the central nervous system may be involved.

Prolactin and growth hormone responses in the amenorrhea-galactorrhea syndrome.

Fifteen patients with hyperprolactinemia, amenorrhea, and galactorrhea were studied; 10 of these patients had apparent tumors. Nine of 12 patients had a suppression of prolactin with oral L-dopa, and all of 4 patients undergoing dopamine infusion had suppression of prolactin. Eleven and 8 patients underwent chlorpromazine stimulation and insulin-induced hypoglycemia, respectively; none responded. Three of the 4 patients did not show a growth hormone response with dopamine infusion, and L-dopa testing failed to achieve a growth hormone response in 7 of 10 patients. The data suggest an intact dopaminergic inhibition of prolactin with exogenous agents. However, inhibition of endogenous dopamine by chlorpromazine failed to elicit a prolactin response. The disordered growth hormone response to dopaminergic agents suggests a central disorder of dopamine generation. The possible implication of these results with respect to the pathogenesis of hyperprolactinemia is discussed.

Radiation-related thyroid carcinoma.

Of 1,825 subjects with a history of head or neck irradiation, 358 (19.6%) were found to have thyroid abnormalities. One hundred sixty-five (9%) had either single or multiple nodules 153 (8.4%) had diffuse thyromegaly, and 40 (2.2%) had had thyroid surgery. Surgery was performed on 113 subjects with nodules; carcinoma was found in 34 (30.1%). Clinical examination of the neck was the most valuable method of detecting abnormalities. Detection of nodules was not significantly enhanced by routine use of thyroid imaging studies. Measurements of levels of serum thyroid-stimulating hormone, thyroxine, triidothyronine resin uptake, and thyroid antibodies were not useful in screening for nodules or carcinoma.

Extrahypothalamic brain prolactin: characterization and evidence for independence from pituitary prolactin.

Prompted by reports of immunohistochemical localization of a prolactin-like immunoreactivity (PLI) within the rat brain, a study was undertaken to define the immunologic and biologic characteristics of this material in extrahypothalamic regions of the rat brain. Ninety-seven percent recovery of rat prolactin standard, added to homogenates of brain parts, insured that neuronal tissue did not interfere with the radioimmunoassay for rat prolactin. PLI was consistently found in the cerebellum, thalamus, brainstem (pons-medulla), hippocampus, cerebral cortex and caudate. Examination of the elution profile of each of the extrahypothalamic brain parts from Sephadex G-75 columns showed that, although a small amount of brain PLI elutes in the vicinity of the anterior pituitary prolactin marker, the bulk of brain-based PLI migrates with the void volume and as late eluting, low molecular weight material. While increasing amounts of brain extracts progressively displaced more 125I-prolactin from antibody binding, the displacement curve was not parallel to that produced by the addition of increasing amounts of anterior pituitary prolactin standards of rat origin. Extracts of various brain parts from hypophysectomized animals, analyzed for biologic activity in the Nb2 lymphoma cell assay, revealed prolactin-like bioactivity, but the bioactivity/immunoreactivity ratio for some of the brain parts was significantly lower than that for pituitary prolactin. Hypophysectomy, which led to the expected fall in serum prolactin to undetectable levels, and restraint stress, which resulted in a statistically significant 4-fold rise in serum prolactin, caused no change in prolactin concentrations in extrahypothalamic brain parts, indicating that brain PLI is regulated independently of pituitary prolactin and of circulating serum prolactin levels.

Radiological assessment of intrasellar prolactin-secreting tumors.

In this study, the value of high resolution computed tomography (CT) in defining prolactin-secreting intrasellar tumors was compared to the value of conventional hypocycloidal polytomography. In all cases, contrast-enhanced coronal CT images were capable of defining these tumors by the demonstration of abnormal dimensions, upward convexity, or regional low density areas in the pituitary gland. The focal regions of decreased density and contrast enhancement correlated consistently with the prolactin-secreting microadenoma location found during surgical removal. Polytomography was not as effective as CT in the diagnostic differentiation of these adenomas.