Possible involvement of A1 receptors in the inhibition of gonadotropin secretion induced by adenosine in rat hemipituitaries in vitro

Abstract

We investigated the participation of A 1 or A 2 receptors in the gonadotrope and their role in the regulation of LH and FSH secretion in adult rat hemipituitary preparations, using adenosine analogues. A dosedependent inhibition of LH and FSH secretion was observed after the administration of graded doses of the R-isomer of phenylisopropyladenosine (R-PIA; 1 nM, 10 nM, 100 nM, 1 µM and 10 µM). The effect of R-PIA (10 nM) was blocked by the addition of 8-cyclopentyltheophylline (CPT), a selective A 1 adenosine receptor antagonist, at the dose of 1 µM. The addition of an A 2 receptor-specific agonist, 5-Nmethylcarboxamidoadenosine (MECA), at the doses of 1 nM to 1 µM had no significant effect on LH or FSH secretion, suggesting the absence of this receptor subtype in the gonadotrope. However, a sharp inhibition of the basal secretion of these gonadotropins was observed after the administration of 10 µM MECA. This effect mimicked the inhibition induced by R-PIA, supporting the hypothesis of the presence of A 1 receptors in the gonadotrope. R-PIA (1 nM to 1 µM) also inhibited the secretion of LH and FSH induced by phospholipase C (0.5 IU/ml) in a dose-dependent manner. These results suggest the presence of A 1 receptors and the absence of A 2 receptors in the gonadotrope. It is possible that the inhibition of LH and FSH secretion resulting from the activation of A 1 receptors may have occurred independently of the increase in membrane phosphoinositide synthesis.

Purinergic signaling in the ovary

“…Furthermore, the anterior pituitary was reported to release ATP, which is rapidly degraded by ectonucleotidases (He et al, ). Indeed, adenosine, acting through the ADORA1 receptor, was shown to inhibit the secretion of the gonadotropins follicle‐stimulating hormone (FSH) and luteinizing hormone (LH) by cells of the anterior pituitary (Picanço‐Diniz et al, ).…”

Purinergic signalling in endocrine organs

“…Adenosine stimulated cells of the hypothalamus-pituitary-adrenal cortical axis [519]. The involvement of A 1 receptors has been described in the inhibition of gonadotrophin secretion of LH and FSH induced by adenosine acting via A 2 in rat hemipituitaries in vitro [414]. A 2 receptors have also been implicated in the stimulatory effects of adenosine on prolactin secretion [415].…”