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Noradrenaline plays a key role in the initiation of ovulation in nonprimate species. A similar noradrenaline role in the primate has not been established experimentally. We utilized the ovariectomized-oestrogen-supplemented (OVX + E) rhesus macaque to examine the effects of intravenous (i.v.) infusion of oestradiol-17beta (E2) on the activity of the brain noradrenaline system. Experiment 1 established the induction of a preovulatory surge-like release of luteinizing hormone in OVX + E monkeys by i.v. infusion of E2 (OVX + E + E2). In experiment 2, a marked increase in hypothalamic microdialysate noradrenaline concentrations occurred after identical E2 infusion into the OVX + E monkeys that were used in experiment 1. In experiment 3, tyrosine hydroxylase (TH) mRNA expression in the locus coeruleus of the brainstem increased at various times after E2 infusion as determined by semiquantitative in situ hybridization. The amount of TH mRNA in OVX + E + E2 animals was higher (P0.05) than that in either the OVX + E or OVX monkeys; no difference was found in the latter two groups. Moreover, selected locus coeruleus sections from E2-infused monkeys were examined for the localization of oestrogen receptors (ER) by in situ hybridization. Both ER-alpha and ER-beta mRNAs were expressed in the locus coeruleus, although the expression was greater for ER-alpha than for ER-beta. We conclude that i.v. infusion of E2, which induces a preovulatory surge-like release of LH, stimulates brain noradrenaline activity; this enhanced activity likely involves an ER-mediated process and is reflected by hypothalamic noradrenaline release and locus coeruleus TH mRNA expression. The results support the concept that noradrenaline can influence the E2-stimulated ovulation in nonhuman primates and that the brainstem is one of the components in this neuroendocrine process.

Pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH) is suppressed by alpha-adrenergic antagonists in ovariectomized (OVX) rabbits, thus suggesting that initiation of GnRH pulses requires the presence of norepinephrine (NE) stimulation. Terminals of NE neurons are located in proximity with GnRH cells in the hypothalamus, including the arcuate nucleus-median eminence (AME) region. Synaptic NE molecules may be catabolized or transported back to NE terminals (i.e. reuptake) via specific NE transporter proteins (NET). Thus, the amount of synaptic NE acting on GnRH cells is a function of the rate of NE release, metabolism and reuptake. Hypothetically, the rise and fall of a GnRH pulse may be associated with the similar fluctuations of synaptic NE release and/or NET activity. To test this hypothesis, we examined the effects of AME administration of desipramine (DMI, a specific NET blocking drug) on GnRH release. First, we delivered 0.2-10 mM doses of DMI continuously for 1 h via an AME microdialysis (microD) system into intact male rabbits. We found that each AME-DMI infusion, between dosages of 1 mM and 10 mM, stimulated a GnRH pulse, and that the size of these GnRH pulses were proportional to the dosage of DMI. To confirm the specificity of DMI on NET, we measured catecholamine content in microD samples by HPLC. The temporal (60 min) DMI induced a pattern of NE release that included a rising limb within the first 20-30 min; although NE returned to baseline values within the period of DMI treatment. Neither epinephrine nor dopamine levels were changed by DMI. Second, a median dose of DMI (5 mM) was given by microD for 60 min in four separate rabbit models: gonadal intact females (F-INT), intact males (M-INT), gonadectomized females (F-GDX) and castrated males (M-GDX). Individual microD samples were measured for NE and GnRH. Regardless of gender or gonadal status, 5 mM of DMI concomitantly induced a pulse-like release of NE and GnRH. Furthermore, the response of GnRH to DMI was greater in GDX rabbits than in INT animals of both genders. Third, we administered DMI (5 mM) for 30 min via a push-pull perfusion (PPP) system during four repeated 90 min intervals, in either F-INT or ovariectomized (F-GDX) females, and measured GnRH in PPP samples. In both F-INT and F-GDX, each DMI challenge induced a GnRH pulse. In F-INT, all sequential DMI-induced GnRH pulses were nearly equal in size. In contrast, in F-GDX, the first DMI-induced GnRH pulse was greater than subsequent ones. Collectively, these observations are consistent with the concept of noradrenergic regulation of pulsatile GnRH release, and we conclude that the temporal activity of NET may be an integral part of the mechanism by which GnRH pulses operate.