Brain angiotensin and the female reproductive cycle

Prevention of metabolic disorders and reproductive performance deficits by the blockade of Angiotensin II AT1 receptor in female rats fed with cafeteria diet

Besides the well-known detrimental effects of obesity on cardiovascular and metabolic function, studies have shown that obesity is also associated with impaired reproductive function in women. Alterations in Angiotensin II (Ang II) have been associated with obesity and with female reproduction. The aim of the present study was to evaluate the reproductive and metabolic effects of Ang II AT1 receptor blockade with losartan in an animal model of obesity, in which female rats were offered a palatable, high calorie diet from weaning to adulthood. Sexual behavior, ovulation rates and preovulatory levels of the hormones estradiol, progesterone, LH and prolactin were analyzed. Retroperitoneal and perigonadal fat pads, triglycerides and cholesterol (total, HDL and LDL), and insulin resistance were analyzed. Losartan prevented increases in fat pad storage, insulin resistance, as well as triglycerides and LDL levels induced by cafeteria diet intake. Losartan also prevented ovulatory deficits and loss of preovulatory surges of progesterone and LH in cafeteria-fed female rats probably through the prevention of the increase in body weight and body fat. No alterations in sexual behavior were observed. These results suggest, for the first time, that Ang II contributes to the development of the deleterious effects of obesity on preovulatory surges of LH and progesterone and on the reduction of ovulation in obese female rats.

Reproductive dysfunction in female rats with renovascular hypertension

BACKGROUND

Hypertension is a major public health epidemic that is highly associated with sexual dysfunction in both men and women. Despite its high prevalence, clinical and animal literature on the underlying mechanisms of sexual dysfunction in hypertensive women is remarkably limited.

METHODS

Using a well-established rodent model of renovascular hypertension-the 2-kidney, 1-clip (2K1C) Goldblatt model-we investigated possible reproductive deficits in female rats. We evaluated several aspects of reproductive function in hypertensive female rats: estrous cycle, sexual behavior, ovulation, and plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol at proestrus afternoon.

RESULTS

Clipping of the left renal artery resulted in dramatic elevations in systolic blood pressure and heart rate. Renovascular hypertension was associated with a delay for reestablishing estrous cyclicity (50% of 2K1C rats failed to resume cycling by 15 days after surgery). In rats that resumed cycling, 2K1C female rats showed a decrease in sexual behavior, evidenced by a decreased lordosis quotient and a reduction in ovulation, as demonstrated by a decreased number of oocytes. Moreover, plasma levels of LH on the proestrus afternoon were reduced in hypertensive female rats, but no changes in estradiol or FSH were observed.

CONCLUSIONS

Our results demonstrate that renovascular hypertension induces an overall decrease in reproductive function in female rats. Most important, our results indicate that the animal model of renovascular hypertension could be used as a relevant tool to understand better the pathophysiological mechanisms involved in the reproductive deficits in women with renovascular hypertension.

Pituitary aminopeptidase activities involved in blood-pressure regulation are modified by dietary cholesterol: sex differences

Given that the existence of a local renin-angiotensin system (RAS) in the pituitary and its participation in the regulation of blood pressure and other biological functions are widely accepted, the aim of this work is to analyze the influence of dietary cholesterol on the activity of the enzymes involved in the metabolism of the effector peptides of the renin-angiotensin system (angiotensin II and III) and vasopressin, in the pituitary of male and female mice fed on a cholesterol-enriched diet (1% cholesterol and 0.5% cholic acid). Soluble and membrane-bound pituitary aminopeptidase A (aspartyl- and glutamyl-aminopeptidase), aminopeptidase M (alanyl-aminopeptidase), aminopeptidase B (arginyl-aminopeptidase) and cystinyl-aminopeptidase activities were fluorimetrically measured. In female mice, cholesterol-enriched diet produced a significant increase in soluble aspartyl- and membrane-bound aspartyl- and glutamyl-aminopeptidase activities, and a significant decrease in membrane-bound alanyl-, arginyl- and cystinyl-aminopeptidase activities. In male mice, after feeding the diet, a significant increase in soluble glutamyl- and membrane-bound arginyl-aminopeptidase activities was observed. Our results indicate differential effects of dietary cholesterol on the metabolism of angiotensin II and III and vasopressin in the pituitary of male and female mice.

Lactation decreases angiotensinogen mRNA expression in the midcaudal arcuate nucleus of the rat brain

In lactating rats, ANG II receptor binding in the arcuate nucleus (ARH) and median eminence is decreased. To further evaluate brain angiotensinergic activity during lactation, we assessed angiotensinogen (AON) mRNA by in situ hybridization in forebrains of day 10 or 11 postpartum lactating and diestrous rats. AON mRNA was abundantly expressed in the ARH, preoptic, suprachiasmatic, supraoptic, paraventricular, and dorsomedial hypothalamic nuclei, and other regions, similar to that reported in male rat brains. AON mRNA levels were decreased 27% in the midcaudal ARH of lactating rats but did not differ between lactating or diestrous rats in any of the other brain areas examined. Immunofluorescence for AON and glial fibrillary acidic protein or tyrosine hydroxylase confirmed that the AON immunoreactivity in the ARH was limited to astrocytes. Confocal microscopy revealed close appositions of AON-positive astrocytes to dopaminergic neurons in the ARH. The decrease in AON mRNA in the midcaudal ARH during lactation coupled with decreased ARH ANG II receptor binding suggests that lactating rats are less subject to ANG II-mediated inhibition of prolactin secretion.

Hormonal and neurotransmitter roles for angiotensin in the regulation of central autonomic function

In this review we present the case for both hormonal and neurotransmitter actions of angiotensin II (ANG) in the control of neuronal excitability in a simple neural pathway involved in central autonomic regulation. We will present both single-cell and whole-animal data highlighting hormonal roles for ANG in controlling the excitability of subfornical organ (SFO) neurons. More controversially we will also present the case for a neurotransmitter role for ANG in SFO neurons in controlling the excitability of identified neurons in the paraventricular nucleus (PVN) of the hypothalamus. In this review we highlight the similarities between the actions of ANG on these two populations of neurons in an attempt to emphasize that whether we call such actions "hormonal" or "neurotransmitter" is largely semantic. In fact such definitions only refer to the method of delivery of the chemical messenger, in this case ANG, to its cellular site of action, in this case the AT1 receptor. We also described in this review some novel concepts that may underlie synthesis, metabolic processing, and co-transmitter actions of ANG in this pathway. We hope that such suggestions may lead ultimately to the development of broader guiding principles to enhance our understanding of the multiplicity of physiological uses for single chemical messengers.

Genetic control of fertility and embryonic waste in the mouse: A rolefor angiotensinogen

The purpose of this study was to evaluate the impact of angiotensinogen gene (Agt) deficiency on reproductive fitness in a rodent model. Mice with 0 (Agt(-/-)), 1 (Agt(-/+)), and 2 (Agt(+/+)) copies of Agt were bred according to the following schemes: 1) Agt(-/-) x Agt(-/-), 2) Agt(-/+) x Agt(-/+), 3) Agt(+/+) x Agt(+/+), and 4) Agt(+/+) female symbol x Agt(-/+) male symbol. There were 4 breeding pairs per scheme. Breedings were time mated. Mice and litters were weighed daily. Southern blotting was used for genotyping. We found that Agt(-/-) breeding pairs had fewer litters (2 [range 1-2] vs. 4 [range 3-5]; P = 0.01), fewer pups per litter (4 [range 1-7] vs. 6 [range 1-10]; P = 0.006), and longer interpregnancy intervals (43 days [range 31-44] vs. 35.5 days [range 22-58]; P = 0.04) compared to wild-type controls. The ratio of postcoital plugs to subsequent litters was 4.0 and 1.2 for Agt(-/-) and Agt(+/+) breedings, respectively (P = 0.03). Median maternal weights during all trimesters of pregnancy were significantly lower for Agt-deficient mice compared to wild-type controls. Among Agt(-/+) x Agt(-/+) breedings, the proportions of Agt(+/+) (n = 17), Agt(-/+) (n = 38), and Agt(-/-) (n = 4) offspring differed significantly from the expected 1:2:1 Mendelian inheritance pattern (P = 0.03). Neonatal survival among the offspring derived from the Agt(-/-) x Agt(-/-) breeding scheme was significantly reduced (P = 0. 001). We conclude that Agt deficiency is associated with an in utero lethal effect, decreased fertility, and impaired neonatal survival.

Effects of age and gender on the AII-induced stimulation of prolactin release and inositol phosphate accumulation in rat anterior pituitary cells in vitro

The stimulatory effects of Angiotensin II (AII) on prolactin secretion and inositol phosphate accumulation were examined in dispersed anterior pituitary cells collected from young (3-4 month), mature (7-8 month) and old (18-20 month) male and female rats. Physiological doses of AII (0.01-10 nM) stimulated prolactin release from cells collected from mature female rats only. This effect was antagonized by pretreatment with Saralasin, an AII receptor antagonist. Significant accumulation of the inositol phosphates was observed in cells obtained from the mature, female donors and this increase preceded the prolactin response. Although there was a small increase in total inositol phosphate accumulation in cells obtained from the old female rats, this was transient and did not coincide with a similar increase in prolactin release. These results indicate that pituitary sensitivity to AII stimulation is related to the age and the gender of the donor animal. The physiological role of pituitary AII needs to be examined in sexually mature female animals.