Norepinephrine is a possible neurotransmitter stimulating pulsatile release of luteinizing hormone-releasing hormone in the rhesus monkey

The hypothesis that norepinephrine (NE) plays a facilitatory role in controlling the pulsatile release of LHRH was tested with a modified push-pull perfusion technique in conscious rhesus monkeys. The in vivo LHRH release in perfusate samples collected from the stalk-median eminence of ovariectomized females was pulsatile and synchronous with pulsatile LH release. Catecholamines measured in aliquots of perfusate samples revealed that in vivo NE release was also pulsatile and was synchronous with LHRH release. Local infusion of NE or methoxamine (an alpha 1-adrenergic stimulant) through a push cannula stimulated LHRH release, while iv injection of prazosin (an alpha 1-adrenergic blocker) suppressed LHRH release. It is concluded that NE is a possible neurotransmitter stimulating pulsatile LHRH release.

Luteinizing hormone releasing hormone (LHRH) neuroterminals mapped using the push-pull perfusion method in the rhesus monkey

In vivo luteinizing hormone releasing hormone (LHRH) release was measured in conscious, ovariectomized rhesus monkeys using a push-pull cannula inserted into the stalk-median eminence, and the relationship between sampling location and LHRH release was examined. Within an individual animal in which multiple experiments were conducted with different cannula placements, LHRH pulse frequency was consistent. In contrast, LHRH pulse amplitude and mean LHRH release varied with cannula tip location in a pattern which reflected the anatomical distribution of LHRH-immunoreactive fibers described for the rhesus monkey. These results suggest that our push-pull perfusion method is reliable for the in vivo measurement of LHRH and perhaps other neuropeptides and/or neurotransmitters, as well.

Steroidogenesis by the immature rhesus monkey ovary in vitro

Primates are believed to have a low level of ovarian steroidogenic activity during prepubertal development. In order to study the rate limiting factors associated with the low level of steroidogenesis, ovaries from prepubertal rhesus monkeys were quartered and incubated for 48 h at 37 C in minimum essential medium. These ovaries secreted 687 +/- 347 pg estradiol/mg ovary and 299 +/- 35 pg progesterone/mg ovary during 48 h of incubation. The addition of 100 ng luteinizing hormone (LH) or 1 mM dibutyryl (Bu)2 cAMP failed to increase significantly estradiol or progesterone secretion. Furthermore, the addition of either progesterone or androstenedione failed to augment estradiol secretion. The presence of either LH or (Bu)2 cAMP with the steroidal substrates also failed to augment estradiol secretion. In contrast, the addition of (Bu)2 cAMP with lipoprotein-derived cholesterol significantly stimulated a two-fold increase in progesterone secretion. The presence of LH in the lipoprotein-supplemented medium failed to augment progesterone secretion. These results suggest that prepubertal monkey ovaries lack the ability to respond to LH, probably due to a lack of gonadotropin receptors or failure of the receptor to stimulate cAMP synthesis. Furthermore, the failure of progesterone and androstenedione to augment estradiol secretion suggests that some cellular components needed to induce aromatase activity are not functional in the prepubertal primate ovary.