Time course of vasopressin and oxytocin secretion after stress in adrenalectomized rats.

To characterize the participation of vasopressin (AVP) and oxytocin (OT) in hypothalamus-pituitary-adrenal regulation after adrenalectomy (ADX), we evaluated corticosterone, ACTH, AVP and OT plasma concentrations and AVP and OT content of the paraventricular nucleus (PVN) at different periods (3 h, 1, 3, 7 and 14 days) in sham or ADX rats under basal conditions and after immobilization stress. ADX animals showed undetectable corticosterone levels, while sham animals showed a marked increase in corticosterone and ACTH 3 h after surgery, then lowering to basal control levels. ADX rats showed high basal ACTH levels with a triphasic response without changes after immobilization. After three hours, the ADX group showed higher OT levels than the sham group. OT was increased after immobilization stress in sham and ADX groups. AVP plasma levels did not change throughout the basal or stress studies in either group. There was a decrease in hypothalamic AVP content 1 and 3 days after ADX under basal and stress conditions. Plasma osmolality showed a significant decrease in the ADX group at 3, 7, and 14 days. In conclusion, there are different pituitary-adrenal axis set points after removal of the glucocorticoid negative feedback. The role of vasopressinergic and oxytocinergic neurons in the ACTH secretion after ADX or immobilization stress appears to differ. Magnocellular AVP is unlikely to contribute to ACTH secretion in response to ADX or immobilization stress. On the other hand, OT is elicited by immobilization stress and might contribute to the ACTH secretion during short-term ADX.     

Polyribosome distribution in regenerating livers of irradiated adrenalectomized rats.

The effect of gamma-radiation (1800 rad) on polyribosome distribution in the regenerating livers of intact and adrenalectomized rats was studied both before and after partial hepatectomy. The animals were divided into four sub-groups: (1) control; (2) irradiated only; (3) partially hepatectomized; and (4) irradiated partially hepatectomized. The relative distribution of lighter oligosomes to heavier polyribosomes was analysed by sucrose density gradient centrifugation (10-40 per cent). Partial hepatectomy by itself increased the proportion of heavier polyribosomes in both intact and adrenalectomized rats. However, when gamma-rays were delivered 2 hours before or 2 hours after partial-hepatectomy, the formation of heavy polyribosomes was decreased for at least 24 hours after hepatectomy in the adrenal intact rats. This depression was not maintained until later times (48 and 72 hours after hepatectomy) when an increase in the proportion of heavy polyribosomes relative to light oligosomes was observed. In addition, irradiation did not measurably affect the distribution of polyribosomes in regenerating hepatocytes of adrenalectomized rats at any time after partial hepatectomy.     

Immunocytochemistry of magnocellular neurons of supraoptic and paraventricular nuclei of normal and Brattleboro rats with vasopressin anti-idiotype antibody

Summary A vasopressin anti-idiotype antibody was generated by immunization with purified IgG of a primary vasopressin antiserum. The anti-idiotype antibody immunostained neurons in the supraoptic and paraventricular nuclei of the hypothalamus of normal and Brattleboro rats. The distribution of immunostained perikarya in these hypothalamic nuclei together with the staining of fibers in median eminence and neural lobe was similar to that observed in normal rats with anti-vasopressin and suggests strongly that vasopressinergic neurons are being stained. Absorption studies with vasopressin and a vasopressin-binding receptor protein further indicate that a receptor associated with vasopressinergic neurons is recognized by the anti-idiotype antibody.Supported by NIH grants ES03239, NS18626 and NSF grant BNS-8310914. D.T.P. is the receipient of RCDA award NS00869     

Renal vasopressin receptor expression and function in rats following spaceflight.

It has been suggested there is a decreased renal responsiveness to vasopressin following spaceflight and that this may be the mechanism for the increased urine flow that is observed following return to normal gravity. In the present study, we have therefore measured vasopressin receptor expression and activity in kidneys taken from rats 1 and 14 days following spaceflight of 15 days duration. Measurements of renal vasopressin V(2) and V(1a) receptor mRNA expression by quantitative RT-PCR demonstrated little difference at either 1 day or at 14 days following return from space. Evaluation of (3)H-labeled arginine vasopressin binding to membranes prepared from kidneys indicated that the majority of the vasopressin receptors were V(2) receptors. Furthermore, the data suggested that binding to vasopressin V(2) or V(1a) receptors was unaltered at 1 day and 14 days following spaceflight. Similarly, the ability of vasopressin to stimulate adenylate cyclase suggested no change in vasopressin V(2) receptor activity in these animals. These data suggest that, whatever changes in fluid and electrolyte metabolism are observed following spaceflight, they are not mediated by changes in vasopressin receptor number or vasopressin-induced stimulation of adenylate cyclase.     

Vasopressin receptor expression in the placenta

The arginine vasopressin (AVP) type 1a receptor (V1a) is well known to mediate vasoconstriction. In pregnancy, blood flow in the placenta is crucial for sustaining normal growth and development of the fetus. This is the first AVP receptor study in the placenta and fetal membranes. The aim was to compare, quantitatively, the level of V1a gene expression with that of a known marker for vascularization, aquaporin 1 (AQP1). V1a and AQP1 gene expression did not correlate; placental V1a mRNA levels were significantly upregulated at 45 and 66+/-1 compared with 27, 100+/-4, and 140 days (term approximately 150 days). V1a mRNA levels were much lower in fetal membranes in which no significant difference across gestation was observed. In situ hybridization histochemistry localized V1a gene expression in the maternal component of the placenta similar to the receptor-binding studies using 125I-labeled [d(CH2)5, sarcosine7] vasopressin. No AVP gene expression was observed in the placenta and fetal membranes, which eliminates local AVP production. This increase in V1a expression at 45 and 66+/-1 days of gestation correlates with the period of maximal placental growth in the sheep and suggests that AVP and V1a receptors may play a hitherto unrecognized role in placental growth, differentiation, and/or function, particularly in the deleterious effects of heat stress, early in pregnancy, on fetal growth.     

Interaction of putative vasopressin receptors in rat brain and bovine pituitary gland with a vasopressin anti-idiotype antibody as revealed by immunoblotting

Vasopressin (AVP)-binding proteins were obtained from rat brain and the anterior and posterior lobes of bovine pituitary glands by (a) preparation of crude membranes, (b) solubilization of membrane proteins, (c) passage through an affinity column containing immobilized AVP, and (d) elution from the column with excess AVP. Gel electrophoresis revealed protein bands of 55 and 62 kilodaltons in rat brain, bovine posterior lobe and, to a far lesser extent, in the anterior lobe, which were similar to those previously identified in rat brain to be associated with AVP binding. Immunoblotting demonstrated that the 55 kilodalton bands of rat brain and bovine pituitary gland were selectively immunoreactive with an AVP anti-idiotype antibody. In addition, immunoreactivity occurred with a 62 kilodalton component of rat brain.     

Calcitonin responses in intact and adrenalectomized rats

The effect of adrenalectomy on the response to exogenously administered calcitonin has been studied in rats. In adrenalectomized rats calcitonin produced a hypocalcemia equivalent to that produced in adrenal intact rats. However, the responses in intact and adrenalectomized rats differed in that recovery from hypocalcemia was delayed by adrenalectomy. Literature data indicate that calcitonin is taken up by the adrenal cortex. Data presented here indicate that adrenal cortical tissue inactivates calcitonin. Thus, the prolongation of the hypocalcemia of calcitonin by adrenalectomy may be due to the removal of an organ that sequesters and degrades the hormone.     

Studies on adrenaline-induced lipolysis in adrenalectomized rats.

In a short-term study, adrenaline-induced lipolysis was less in adrenalectomized rats than in controls, though the cyclic AMP accumulation was not different. In adrenalectomized rats treated with corticosterone, lipase activity was as low as in untreated adrenalectomized rats, although adrenaline-induced lipolysis was not reduced. In a long-term study, no reduction in adrenaline-induced lipolysis or cyclic AMP accumulation was observed in adrenalectomized rats. The mechanism of the effect of adrenalectomy on adrenaline-induced lipolysis is discussed on the basis of these results.