Michael Berelowitz

Hormonal Regulation of Rat Hypothalamic Neuropeptide mRNAs: Effect of Hypophysectomy and Hormone Replacement on Growth-Hormone-Releasing Factor, Somatostatin and the Insulin-Like Growth Factors

Hormonal feedback regulation of hypothalamic peptides putatively involved in growth hormone (GH) regulation has been studied by measurement of steady-state mRNA levels in male hypophysectomized rats with or without thyroid hormone, corticosterone, testosterone or GH replacement. Hypothalamic GH-releasing factor (GRF) mRNA levels increased progressively following hypophysectomy to 420% of sham levels after 15 days while hypothalamic insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II) mRNA levels decreased to less than 40% of sham levels. Whole hypothalamic somatostatin mRNA levels were not significantly different from sham. One week of continuous GH infusion restored hypothalamic IGF-I mRNA to levels (95%) indistinguishable from those in sham-operated controls but had no effect on either IGF-II or GRF mRNA. Thyroid hormone, corticosterone and testosterone treatment without GH had no effect on the hypophysectomy-induced reduction of either IGF-I or IGF-II mRNA levels but reversed the elevation of GRF mRNA. We conclude that hypothalamic IGF-I may be involved in GH feedback regulation and thus may function as a hypothalamic modulator of GH. In contrast, IGF-II may be regulated by one of the pituitary trophic hormones but not by GH or the target hormones tested. Finally, hypothalamic GRF mRNA regulation appears to be complex and may include target hormone feedback.

Effect of ventromedial hypothalamic lesions on the secretion of somatostatin, insulin, and glucagon by the perfused rat pancreas

Abstract Somatostatin, insulin, and glucagon secretion by the perfused pancreas were studied in adult female rats 10 days after ventromedial hypothalamic (VMH) lesions and in sham operated controls to assess the role of their hypothalamic control. Insulin secretion was significantly greater in VMH-lesioned rats both under basal conditions and after stimulation by theophylline and arginine plus theophylline. Basal glucagon secretion was greater in VMH-lesioned rats as was the glucagon response to theophylline alone and in combination with arginine. Basal somatostatin secretion was similar in VMH and control rats but somatostatin secretion induced by theophylline and by arginine plus theophylline was significantly increased in VMH-lesioned rats. Both the pancreatic content and concentration of somatostatin were increased in VMH-lesioned rats. These results indicate the presence of hyperresponsiveness of A, B, and D cells following VMH destruction and provide new evidence for a role of the hypothalamus in the regulation of pancreatic somatostatin secretion.

Adenosquamous carcinoma of the colon presenting with hypercalcemia

A rare adenosquamous carcinoma of the colon occurred in a 41‐year‐old patient. Its presentation with hypercalcemia, in the absence of osseous metastases, has not been described previously. The hypercalcemia in this case was due to the elaboration of a parathyroid hormone‐like substance by the tumor. The general characteristics of primary adenosquamous and squamous cell carcinomas of the colon are presented. These tumors present with advanced disease, in younger patients, and follow a highly aggressive course, as compared with adenocarcinomas of the colon. The cause of the malignancies, in the light of current theories regarding their genesis, is discussed.

Pituitary and hypothalamic insulin-like growth factor-I (IGF-I) and IGF-I receptor expression in food-deprived rats

The present study was designed to evaluate a possible role for the insulin-like growth factor-I (IGF-I) system in mediating the suppression of growth hormone (GH) secretion observed in food-deprived rats by measuring IGF-I mRNA, receptor concentration and receptor mRNA in neuroendocrine tissues (hypothalamus and pituitary). Rats were deprived of food (food-deprived) for 72 h or had free access to food (fed). Tissues were processed for measurement of steady-state levels of: (a) IGF-I and IGF-I receptor mRNA (by solution hybridization/RNase protection assay); (b) IGF-I in serum and tissue extracts (by RIA) and (c) IGF-I displaceable [125I]IGF-I binding to plasma membrane preparations. Food deprivation resulted in decreased serum and liver levels of IGF-I. Kidney IGF-I mRNA levels were reduced 80% in food-deprived rats with a concomitant increase in IGF-I receptor concentration and mRNA levels. Refeeding of food-deprived rats fully normalized these perturbations. Pituitary IGF-I content was reduced 50% in food-deprived rats while IGF-I mRNA levels were unaffected. A modest increase was seen in pituitary IGF-I receptor concentration; however, IGF-I receptor mRNA levels were not changed. Hypothalamic IGF-I mRNA content was reduced in 72 h food-deprived rats while IGF-I receptor binding capacity and mRNA were unaffected. In conclusion, IGF-I mRNA levels are decreased in liver, kidney and hypothalamus together with a reduction in plasma IGF-I in food-deprived rats but is unaffected in anterior pituitary. IGF-I receptor gene expression and binding capacity are coordinately regulated in kidney and hypothalamus, but not in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Ligand Binding and Functional Properties of the Rat Somatostatin Receptor SSTR4 Stably Expressed in Chinese Hamster Ovary Cells.

Somatostatin (SS14) is an important regulator of endocrine and brain function exerting its action after binding to high-affinity membrane receptor subtypes. Its diverse physiological activities include inhibition of hormone secretion from pituitary, pancreas, and gut. In the CNS, SS14 acting as a neurotransmitter/neuromodulator exerts inhibitory effects on neural function. Recently, three SS14 receptor genes, SSTR1, SSTR2, and SSTR3, have been cloned and characterized. We have cloned and characterized a novel fourth member of this gene family from a rat genomic library, SSTR4, which is expressed predominantly in neural tissue. When stably expressed in CHO-K1 cells, SSTR4 binds SS14 and SS28 with high affinity; however, the SS14 analogs SMS 201-995 and MK 678 failed to displace specific binding. High-affinity agonist binding was diminished by prior exposure to both GTPgammaS and pertussis toxin (PTX) but was not effected following agonist pretreatment, indicating that SSTR4 is coupled to a PTX-sensitive G-protein but does not desensitize. SSTR4 expressed in CHO cells is coupled by a PTX-sensitive G-protein to inhibition of adenylyl cyclase since treatment of transfected cells with SS14 resulted in the inhibition of forskolin-stimulated cAMP accumulation, an effect that was abolished by PTX treatment. The cloning of four SS14 receptor subtypes provide molecular probes for structure-function studies and for identifying those particular subtypes responsible for mediating the diverse physiological action of SS14.

Acute effects of alloxan- and streptozotocin-induced insulin deficiency on somatostatin and glucagon secretion by the perfused isolated rat pancreatico-duodenal preparation

SummaryThe secretion of somatostatin and glucagon by the perfused rat pancreatico-duodenal preparation was examined in situ under control conditions and after the induction of acute insulin deficiency by alloxan or streptozotocin. A 10 min 0.625 mmol/l alloxan perfusion resulted in an immediate and transient increase in basal insulin and glucagon release and a slightly delayed and persistent increase in basal somatostatin secretion. The insulin responses to 16.7 mmol/l glucose, 1 mmol/l theophylline, and 19 mmol/l arginine alone or in combination were virtually eliminated by alloxan treatment, Somatostatin secretion in response to the stimuli was completely inhibited or markedly attenuated. The glucagon-suppressive effect of glucose was unaltered by alloxan and the stimulatory effect of arginine was enhanced. Addition of 1 μg/ml porcine insulin to the perfusion medium did not modify the alterations in somatostatin and glucagon responses to arginine. Streptozotocin treatment 90 min prior to the onset of perfusion resulted in changes in somatostatin, glucagon, and insulin responses to glucose and arginine similar to those of alloxan. The present results are consistent with an effect of alloxan and streptozotocin on the D cell similar to that on the B cell, namely, interference with a glucose-mediated effect on hormone secretion.

The effect of intravenous growth hormone infusion on cerebrospinal fluid somatostatin levels in the rhesus monkey

CSF was continuously withdrawn over 13 days from the cervical subarachnoid space of two rhesus monkeys during the intravenous infusion of saline or human growth hormone (GH) and samples collected during sequential 2 h periods were assayed for somatostatin (SRIF). SRIF-like immunoreactivity (SRIF-LI) concentrations were decreased during GH infusion as compared to saline infusion (P less than 0.005) and the maximal effect occurred during the hours of darkness (18.00-06.00 h). Since in vivo GH administration stimulates hypothalamic SRIF-LI release, CSF SRIF-LI does not appear to be derived primarily from the hypothalamus but rather from extrahypothalamic brain by a mechanism inhibited by GH.

Localization of prepro-growth hormone releasing factor mRNA in rat brain and regulation of its content by food deprivation and experimental diabetes

Growth hormone releasing factor (GRF) is the principal stimulatory hypothalamic neuropeptide controlling growth hormone (GH) secretion from pituitary somatotrophs. In this study we examined the hypothalamic and extrahypothalamic sites of preproGRF mRNA expression using both in situ hybridization and nuclease protection techniques. Each of these techniques confirmed that the principal site of GRF expression in CNS is within the hypothalamic arcuate nucleus with an additional population of neurons lying in the periventromedial region of the hypothalamus. PreproGRF mRNA was also detected at low levels in paraventricular and supraoptic nuclei, in piriform and neocortex, hippocampus, olfactory bulb, striatum, and brain stem, but not in anterior pituitary. However, the levels of preproGRF mRNA in these latter brain regions were approximately 20- to 50-fold lower than levels in whole hypothalamus. To extend previous observations, we then determined which brain loci modulate preproGRF mRNA levels in response to food deprivation or experimental diabetes mellitus. PreproGRF mRNA levels in both arcuate and periventromedial hypothalamic neurons declined 3- to 5-fold following food deprivation or streptozotocin-induced diabetes mellitus while the number of preproGRF expressing neurons was relatively unchanged in each experimental protocol; however, hybridization signal in piriform cortex and hippocampus was not affected by either experimental protocol. These data implicate two hypothalamic neuronal populations in modulating GH secretion and suggest specific modulation of hypothalamic preproGRF mRNA levels by food deprivation and diabetes.

Insulin-Like Growth Factor-I and Insulin-Like Growth Factor Binding Proteins in the Zucker Fatty Rat: A Case for Differential Tissue Regulation

Obesity is one of the most common health care problems in the Western world.1 It is associated with hypertension, hyperlipidemia and a predisposition to Type II Diabetes Mellitus, which probably accounts, in part, for the high risk these patients have of accelerated atherosclerosis. Given the numbers of people affected and the predisposition these patients have to multiple medical problems, an understanding of the pathophysiology involved in the causes for, and perpetuation of, obesity would aid our ability to possibly prevent and more effectively treat this disease.

Hormonal Feedback Regulation of Brain IGF-I and IGF-II Gene Expression

Release of anterior pituitary hormones is mediated by peptides produced by secretory neurons in the hypothalamus or preoptic area. The releasing or inhibiting factors are stored in nerve endings that lie in the median eminence and are secreted as the result of electrical activity. The hypothalamic peptides then travel through the portal system to the anterior pituitary where they interact with specific surface receptors to trigger release of pituitary trophic hormones. These, in turn, regulate physiologic processes elsewhere in the body either directly or indirectly through release of target gland hormones.