Fluctuations In Ovarian Hormones Research Articles

Ovarian hormone effects on activity, glucoregulation and thyroid hormones in the rat

Ovarian hormonal influences on the range of physiological and behavioral variables which combine to affect overall energy balance are poorly delineated. In the present study 4 groups of virgin, female rats (intact, ovariectomized, ovariectomized with estrogen replacement and ovariectomized with estrogen plus progesterone) were allowed access to running wheels and activity; food intake and weight gain were measured initially under food restricted, then under ad lib conditions. Serum insulin, glucose, thyroxine (T 4) and triiodothyronine (T 4) were determined on trunk blood samples obtained at the end of the experiment. Ovariectomy resulted in an increased rate of weight gain through reduced activity and T 3 but food intake was unchanged. Insulin levels were greatly reduced. Estrogen replacement restored activity to the intact group's level and normalized weight gain. Insulin and T 3 were also raised to control levels but T 4 was reduced as was serum glucose. Estrogen plus progesterone replacement reduced weight gain markedly and increased T 3 with normal T 4. Despite the lower body weight this group was hyperglycemic and hyperinsulinemic suggesting insulin resistance. The results have important implications for the glucoregulatory and energy balance perturbations of ovarian hormone fluctuations and focus particularly on progesterone.

Relationship between endogenous opioids and the oestrous cycle in the rat

The aim of this study was twofold: (1) to document changes in levels of immunoreactive beta-endorphin (Ir-beta-EP) in the hypothalamus, anterior pituitary gland, neurointermediate lobe and plasma during the oestrous cycle of the rat and (2) to investigate stress-induced changes in plasma Ir-beta-EP at different stages of the oestrous cycle. Evidence was found that Ir-beta-EP levels in the hypothalamus, anterior pituitary gland and plasma are not constant during the oestrous cycle and that the Ir-beta-EP response to stress is a function of the phase of the oestrous cycle at which stress is applied. It is suggested that fluctuations in ovarian hormones may influence oestrous Ir-beta-EP levels both under normal conditions and after exposure to stress.

Responses mediated by adrenoceptors in the separated layers of the myometrium and in the costo-uterine muscle of the guinea pig during the estrous cycle.

The mechanical responses of field-stimulated preparations of the longitudinal and circular myometrium, and of the costo-uterine muscle of the guinea pig to adrenoceptor agonists have been examined on Days 1, 4, 10 and 15-16 of the estrous cycle. The alpha-adrenoceptor agonist, phenylephrine, was exclusively excitatory in all three preparations taken from animals at each of the cycle days studied. Concentration-response curves for phenylephrine in all three tissues were unaffected by the fluctuations in ovarian hormones occurring during the estrous cycle. Isoproterenol (1 nmol/1-5 mumol/1) usually inhibited field-stimulation-induced contractions of the longitudinal uterine layer and the costo-uterine muscle; higher doses usually caused enhancement of contractions. In neither tissue did the potency or maximum effect of this inhibitory agonist differ at differing cycle stages. In the circular myometrium, the inhibitory effects of isoproterenol were less consistently observed, particularly in preparations taken at proestrus (Days 15-16). It is concluded that, except perhaps in the circular myometrium at proestrus, the fluctuations in ovarian hormones occurring during the estrous cycle in this species are insufficient to modify uterine responses mediated via alpha- and beta-adrenoceptors. It remains to be established whether the steroid hormones are capable of modulating responses mediated by adrenoceptors in the costo-uterine muscle.

Effects of the menstrual cycle, social grouping, and exogenous progesterone on heterosexual interaction in laboratory housed stumptail macaques (M. arctoides)

The effects of endogenous fluctuations in ovarian hormones during the female's menstrual cycle on heterosexual interaction was studied in groups of stumptail macaques. When 5 different trios of females were paired for 5 consecutive weeks with each of 5 males no aspect of male-female interaction changed as a function of phase of the menstrual cycle. Moreover, males usually preferred to copulate with the same female of each trio in consecutive tests, regardless of the ovarian condition of any of the females. It appeared that the most dominant females in the trios were sexually most preferred. Subcutaneous implantation of silastic capsules containing progesterone into the sexually most preferred females of each trio affected neither the males' sexual preference, nor the behavior of these females, nor the behavior of sexually non-preferred females in each trio. Likewise, progesterone in sexually preferred females had no effect on male-female interaction in pair tests. It is concluded that in stumptail macaques social factors are more important than ovarian hormones in regulating heterosexual interaction.

Cylical fluctuations in reflexive oxytocin release during the estrous cycle of the goat.

Elevations in the circulating level of oxytocin resulting from stimulation of the vagina were determined repeatedly in each of 23 estrous cycles. To delineate the course of each cycle, the day of behavioral estrus was determined and radioimmunoassayable serum progesterone was measured every 2 days. Vaginal stimulation induced greater elevations in the level of oxytocin near the time of estrus and during the early luteal phase than during periods characterized by maximal concentrations of progesterone. Elevations averaged 25.2 ± 8.8 MU/mI plasma in the early luteal phase and then declined progressively, reaching a minimum of 4.2 ± 1.7 MU/mI shortly before progesterone levels fell prior to estrus. This cyclic variation in the oxytocin-elevating effect of vaginal stimulation, viewed in the light of previous studies that have shown strong effects of exogenous ovarian steroids on oxytocin release, suggests that fluctuations in endogenous ovarian hormones during the estrous cycle may influence the oxyotocin secretory mechanism.