Hypothalamic adrenergic activity precedes the preovulatory luteinizing hormone surge in the rat

The neuroendocrine physiology of female reproductive aging: An update

The transition into menopause is a complex process that affects fertility and increases the risk for a number of health problems in aging women that include, but are not limited to osteoporosis, heart disease, diabetes mellitus and cognitive dysfunction. Improved nutrition and enhanced access to medical care have increased the average lifespan for women in developed countries, and many will spend more than one-third of their life in a post-menopausal state. Epidemiological studies indicate that a delayed natural menopause confers longevity and decelerates the appearance of much age-related morbidity, suggesting that developing treatments to delay menopause would significantly improve quality of life for women. Although menopause is ultimately defined by ovarian follicular exhaustion, several lines of scientific evidence in humans and animals now suggest that dysregulation of estradiol feedback mechanisms and hypothalamic-pituitary dysfunction contributes to the onset and progression of reproductive senescence, independent of ovarian failure. This article provides a brief update on our current understanding of the role of the hypothalamic-pituitary axis in the onset of and transition into female reproductive senescence.

Atrazine and reproductive function: mode and mechanism of action studies

Atrazine, a chlorotriazine herbicide, is used to control annual grasses and broadleaf weeds. In this review, we summarize our laboratory's work evaluating the neuroendocrine toxicity of atrazine (and related chlorotriazines) from an historic perspective. We provide the rationale for our work as we have endeavored to determine: 1) the underlying reproductive changes leading to the development of mammary gland tumors in the atrazine-exposed female rat; 2) the cascade of physiological events that are responsible for these changes (i.e., the mode of action for mammary tumors); 3) the potential cellular mechanisms involving adverse effects of atrazine; and 4) the range of reproductive alterations associated with this pesticide.

Interactions between opioid peptides and adrenaline-containing neurons modulate luteinizing hormone secretion in male rats

Abstract There is increasing evidence that the opioid inhibition of luteinizing hormone (LH) secretion is mediated, at least in part, by catecholaminergic mechanisms. This study determined the effects of selective manipulation of noradrenergic and adrenergic systems on the ability of opiate receptor blockade to induce the release of LH in adult male rats. Selective depletion of hypothalamic noradrenaline levels by 80% following 6-hydroxydopamine infusions into the central tegmental tract did not alter the 2- to 3-fold increase in serum LH levels following opiate receptor blockade with naloxone (2.5 mg/kg). In contrast, both selective depletion of hypothalamic adrenaline by prior treatment with the phenylethanolamine N-methyltransferase inhibitor, LY134046 (2 x 50 mg/kg) and non-selective depletion of all three catecholamines with alpha-methyl-p-tyrosine (250 mg/kg), abolished the naloxone-induced increase in LH. These results suggest that the inhibition of LH secretion by endogenous opioid peptides is influenced by catecholaminergic neurotransmission and further support the view that adrenaline rather than noradrenaline or dopamine is of importance in this context.

Adrenaline concentration and turnover in the arcuate nucleus and median eminence during the critical period in the rat

Previous work has shown a relatively high turnover of adrenaline in the mediobasal hypothalamus during the critical period (15.00-17.00 h) of the proestrous rat. We now report that this high level of adrenergic activity can be detected in the median eminence (turnover rate 1.62 +/- 0.36 pg/micrograms protein/h) rather than the arcuate nucleus (turnover rate 0.18 +/- 0.32 pg/micrograms protein/h). In addition the median eminence was isolated as medial and lateral components and determination of catecholamine concentrations revealed a greater proportion of adrenaline (A) (59%) in the lateral median eminence whereas a larger proportion of dopamine (60%) was found in medial median eminence.