G. Folly

Dissociation of presynaptic α2-adrenoceptors following prazosin administration: Presynaptic effect of prazosin

Evidence has been obtained that prazosin possesses a presynaptic alpha 2-adrenoceptor blocking action in the rat was deferens preparation stimulated at 1 Hz. In the presence of prazosin yohimbine failed to affect the presynaptic alpha 2-adrenoceptor stimulatory effect of 1-noradrenaline while the effect of xylazine was almost completely abolished. It is therefore suggested that there are two kinetically different prejunctional alpha 2-adrenoceptor sites.

Long-term salt loading impairs pituitary responsiveness to ACTH secretagogues and stress in rats.

Male Wistar rats were allowed to drink tap water ad lib (W), 2% saline (S) or 2% saline containing dexamethasone (S + D, 1 mg/l) for 7 days. On the 8th day rats were subjected to a 3-min ether stress. Plasma ACTH, corticosterone and prolactin concentrations were determined before and after ether exposure. Prestress concentrations of plasma ACTH were low and did not vary among the three groups. In response to ether stress W rats exhibited twice as high plasma ACTH concentrations as did S rats. Rats of the S + D group exhibited a small but statistically significant ACTH response. Plasma corticosterone concentration in S rats was increased while in S + D rats was significantly decreased under resting conditions compared to that in W rats. Ether stress caused large increases in plasma corticosterone concentrations in W and S rats while a small but statistically significant increase was observed in S + D rats. Prolactin responses to ether were smaller in groups S and S + D than in group W. To test whether the decreased ACTH response to ether exposure was a result of a decreased sensitivity of corticotrope cells to corticotropin releasing factor (CRF)-41 or arginine vasopressin (AVP), adenohypophysial fragments from W, S and S + D rats were incubated in the presence of different doses of CRF-41 or AVP. Pituitary fragments obtained from W rats secreted larger amounts of ACTH than did pituitaries from S rats in response to either CRF-41 or AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of ACTH, β‐endorphin and α‐melanocyte stimulating hormone in relation to the corticosteroid production of isolated rat adrenocortical zona fasciculata and zona glomerulosa cells

The combined effects of ACTH, β‐endorphin (β‐EP) and α‐MSH were studied on the corticosteroidogenesis or isolated rat adrenocortical zona fasciculata and zona glomerulosa cells. β‐EP potentiated the effects of ACTH and α‐MSH on the zona fasciculata corticosterone production but inhibited those on the zona glomerulosa aldosterone production. β‐EP did not affect the combined action of 4×10−11 M ACTH and 5×10−9 M α‐MSH on the zona fasciculata or the zona glomerulosa cells, but it inhibited the stimulatory action of the combination of 1.6×10−10 M ACTH and 10−9 M α‐MSH on the zona glomerulosa aldosterone production. An interaction of ACTH, β‐EP and α‐MSH in relation to the zona fasciculata and zona glomerulosa corticosteroid production was found.