To date, there are no vasopressin (VP) agonists that exhibit a high affinity and selectivity for the VP V1b receptor with respect to the V1a, V2, and oxytocin receptors. In this study, we describe the synthesis and pharmacological properties of [1-deamino-4-cyclohexylalanine] arginine vasopressin (d[Cha4]AVP). Binding experiments performed on various membrane preparations revealed that d[Cha(4)]AVP exhibits a nanomolar affinity for V1b receptors from various mammalian species (rat, bovine, human). It exhibits high V1b/V1a and V1b/oxytocin selectivity for rat, human, and bovine receptors. Furthermore, it exhibits high V1b/V2 specificity for both bovine and human vasopressin receptors. Functional studies performed on biological models that naturally express V1b receptors indicate that d[Cha4]AVP is an agonist. Like VP, it stimulated basal and corticotropin-releasing factor-stimulated ACTH secretion and basal catecholamine release from rat anterior pituitary and bovine chromaffin cells, respectively. In vivo experiments performed in rat revealed that d[Cha4]AVP was able to stimulate both ACTH and corticosterone secretion and exhibits negligible vasopressor activity. It retains about 30% of the antidiuretic activity of VP. This long-sought selective VP V1b receptor ligand with nanomolar affinity will allow a better understanding of V1b-mediated VP physiological effects and is a promising new tool for V1b receptor structure-function studies.

Bilateral adrenalectomy (ADX) leads to increased ACTH synthesis and secretion. It is thought that endogenous glucocorticoids exert a feedback mechanism at both pituitary and brain levels. The present study has been performed in order to determine the effect of ADX on the release of hypothalamic neuropeptides with corticotropin-releasing activity (CRA) and if there exists a median eminence site of glucocorticoid action to regulate hypothalamic-pituitary-adrenal (HPA) function. Adrenalectomized and sham-operated male rats were killed at different periods after surgery (2, 5, 7 and 14 days) and trunk blood was collected for ACTH and corticosterone (B) concentrations measurement. Brain (median eminence, ME; and medial basal hypothalamus, MBH) and pituitary (anterior lobe, AP; and neurointermediate lobe, ) tissues were dissected in order to evaluate either peptide content or in vitro hormone release. The results indicate that ADX blunted plasma B levels and increased AP ACTH content and secretion in a time-related fashion up to the 14th day. ADX significantly decreased both CRF and CRA contents in the ME at all periods studied; ME arginine-vasopressin (AVP) increased 7 and 14 days after ADX. MBH CRF decreased after ADX, but returned to sham value 2 weeks later; similarly, MBH AVP decreased at all periods after ADX. Removal of endogenous glucocorticoids did not vary neither oxytocin (OXY) content in the ME and MBH nor AVP and OXY contents in the . In our superfusion experiments, we found that ADX increased basal AVP release and did not change spontaneous CRF secretion from ME terminals. Dexamethasone (Dxm, 10 nM) diminished AVP but not CRF output by ME tissues from adrenalectomized rats. A direct relationship was found between ME CRF and 28 mlí KC1 (hK+)-induced CRF release by MEs from adrenalectomized rats. ME fragments from adrenalectomized rats were hyperresponsive to kH⁺ stimulation of AVP release. Dxm (10 nM) decreased the hK+ -evoked CRF and AVP release by MEs from adrenalectomized rats. ADX and dexamethasone treatment did not influence basal and hK⁺-elicited ME OXY release. Additionally, a rapid glucocorticoid inhibitory effect on ACTH secretion by isolated AP cells from both sham and adrenalectomized rats was found, and an in vitro corticotrope hyporesponse to 0.63 nM CRF and 9.25 nM AVP stimulation during several days after ADX. We conclude that ADX: (a) increases AP ACTH synthesis and secretion by activating the CRF and AVP neurosecretory systems; (b) induces a hypersecretion of ME AVP under basal and hK+-stimulated conditions; (c) induces an ME site of glucocorticoid action to inhibit CRF and AVP release; (d) decreases the corticotrope response to specific stimulation for several days, and (e) influences neither the hypothalamic-median eminence OXY nor AVP and OXY system. These results further suggest that the ME is an important site of glucocorticoid action to regulate HPA function.

Cytokines secreted by bacterial endotoxin-activated immune cells are substances known to stimulate the hypothalamo-pituitary-adrenal (HPA) axis function. The present study was designed to better understand the effect of different mediators of inflammation, such as cytokines and histamine, on the acute HPA axis response induced by administration of a single dose of bacterial lipopolysaccharide (LPS) in adult, male, BALB/c mice. Two different experimental designs were set up. In the first design, mice (n = 8–11 per group) were injected i.p. with LPS (90 µg/kg body weight) and killed by decapitation 2 or 6 h after treatment. Additional groups of mice were pretreated i.p. 12 h before LPS treatment with: (a) 3–4 mg IgG/kg body weight of either an anti-tumor necrosis factor-α (TNF)-α, anti-interleukin (IL)-1β- or IL-6 serum; (b) IL-1 receptor antagonist (IL-1ra) (120 µg/kg body weight) immediately before LPS and also 3 h later (when animals were killed 6 h after LPS injection), or (c) 182 µg/kg body weight of clemastine, an antagonist of H₁ histaminergic receptors, 2 h before LPS treatment; animals were killed in a similar fashion to that described for treatment with LPS alone. In the second experimental design, mice were pretreated (i.p., 10 mg/kg body weight, 30 min before administration of a similar dose of LPS) with different blockers of histaminergic pathway function such as: (a) mepyramine, another anti-H₁, (b) cimetidine, an H₂ receptor blocker, and (c) Rα-methylhistamine dihydrochloride, an H₃ presynaptic receptor agonist which inhibits histamine synthesis and output. These animals were then killed by decapitation 40 min after endotoxin treatment. After decapitation, trunk blood was collected for further determination of plasma levels of both ACTH and corticosterone (B) by specific assays. The results indicate that plasma levels of both ACTH and B were several-fold increased over baseline, 2 and 6 h after LPS administration. Two hours, the effect of LPS on ACTH output was not modified by pretreatment with anti-IL-1β IgG, anti-IL-6 IgG, anti-TNF-α IgG nor with IL-1ra, although IL-1ra treatment was able to fully block the IL-1β (35 µg/kg body weight)-stimulated HPA axis function, 1 and 2 h after cytokine administration. Six hours after LPS administration, anti-IL-1β and anti-TNF-α IgGs were both able to significantly reduce HPA axis response to the endotoxins, whereas anti-IL6 IgG had no effect. Anti-IL-1β IgG reduced only B secretion, whereas anti-TNF-α IgG decreased both ACTH and B secretion. The blockade of histaminergic pathway functions did not impede the LPS-induced ACTH and B release regardless of the product employed. The present results indicate that TNF-α, and to a lesser extent IL-1β, are the most relevant cytokines involved in HPA axis response to endotoxin administration. Our data also suggest that, in mice, HPA axis activation after infection appeared to be independent of stimualtion of the histaminergic pathway.

Hypothalamic neuropeptide Y (NPY) plays a central role in the control of food intake, energy balance, and modulation of neuroendocrine functions. In particular, an increase in NPY expression participates in the inhibition of the reproductive activity under poor nutritional conditions. The present study was designed to evaluate further the involvement of the Y1 subtype of NPY receptors in these effects. Food intake, body weight gain, and the onset of puberty were studied in groups of wild-type and Y1 deficient mice that were either fed ad libitum or subjected to a 30% restriction in food intake. This moderate feeding restriction induced a similar deficit in body weight gain in wild-type and in Y1 knockout mice. However, although wild-type mice experienced the expected delay of puberty, all mice in the food restriction group and lacking Y1 could go through puberty over the time of the experiment despite decreases in circulating leptin levels and increases in hypothalamic NPY expression. This observation demonstrates that the absence of Y1 impairs the perception of decreasing energy stores by the gonadotrope axis, demonstrating a physiological role for Y1 in the sensing of endogenous metabolic parameters by the hypothalamus.

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