OVX-E2 Rats Research Articles

Effects of physical training on body composition and organ weights in ovariectomized and hyperestrogenic rats.

To investigate whether regular endurance-type exercise can benefit rats submitted to a model of ovariectomy (OVX)-induced obesity with or without estrogen replacement. OVX Sprague-Dawley rats were compared to an ovariectomized-estradiol-treated group (OVXE2) and a Sham-operated (Sham) group. Each of these groups were subdivided into a sedentary and a treadmill-trained (8 wk) group. An experimental study in which various parameters, including fat depots, blood lipids and several organ weights were measured. Plasma levels of 17beta-estradiol and uterus weights were significantly (P<0.05) lower in OVX compared to Sham and significantly (P<0.01) higher in OVXE2 (hyperestrogenic) compared to Sham rats. Body weights were significantly (P<0.01) different among groups, in the following decreasing order: OVX, Sham and OVXE2. The average daily food intake and food efficiency were significantly (P<0.01) increased in OVX compared to Sham, whereas estradiol treatment diminished this effect (P<0.01). Exercise training did not alter any of the above-mentioned variables in any of the three estrogen groups. Mesenteric and subcutaneous fat weights were significantly (P<0.01) increased by OVX. This increase was abolished by estrogen replacement or by exercise training. Exercise training also decreased fat weights in OVXE2 and Sham rats. OVX resulted in a decrease in the weights of several other tissues (femur, heart, lungs, liver and adrenal glands) while hyperestrogenic replacement resulted in an increase in weight of all measured tissues. Aside from fat depots, exercise training did not affect any of the tissue weights with the exception for an increase in the weight of the plantaris muscle and adrenal glands and a decrease in lung weight in all three estrogen groups. In OVX animals, exercise training may bring about positive changes in body composition (ie reduction in fat weights) despite an ovariectomy-induced increase in body weight.

LH subunit mRNA concentrations during LH surge in ovariectomized estradiol-replaced rats.

In cycling rats, pituitary concentrations of luteinizing hormone (LH) beta-subunit mRNA increase two- to threefold before the afternoon proestrus LH surge without a corresponding increase in alpha-subunit mRNA. Estradiol (E2) treatment is known to allow expression of daily LH surges in ovariectomized (OVX) rats, and the timing, magnitude, and duration of LH secretion is similar to the LH surge on proestrus. The present study was conducted to examine whether the regulation of LH subunit mRNAs during the LH surge in OVX-E2-treated rats is similar to that present on proestrus. Female Holtzman rats were OVX and Silastic implants containing E2 were inserted subcutaneously under ether anesthesia. Some animals received bromocriptine (0.6 mg sc, twice/day beginning 1 h before surgery). On the 2nd day after surgery, groups of animals (n = 4-10/group) were decapitated at intervals between 1000 and 2100. LH and prolactin (PRL) levels were measured in trunk blood. LH subunit mRNA concentrations in the pituitaries were measured by dot-blot hybridization assay. In OVX-E2 rats the LH surge occurred at 1830 and was accompanied by a selective twofold increase in alpha-subunit mRNA (from 266 +/- 18 to 459 +/- 61 pg cDNA bound/100 micrograms pituitary DNA) and maximum values were present at 1730. LH beta-subunit mRNA (m = 29 +/- 1 pg cDNA bound/100 micrograms pituitary DNA) was unchanged throughout the day. Bromocriptine treatment resulted in the suppression of serum PRL (m = 23 +/- 2 ng/ml) and the LH surge was delayed by 1-1.5 h and somewhat blunted.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of pituitary gonadotropin-releasing hormone (GnRH) receptors by pulsatile GnRH in female rats: effects of estradiol and prolactin.

GnRH has been shown to modulate the concentration of its own pituitary receptors (GnRH-R), and changes in GnRH-R during the rat estrous cycle may reflect changes in GnRH secretion. To examine the relationship between GnRH and GnRH-R in female rats, we measured GnRH-R and serum gonadotropin responses to pulsatile GnRH in restrained ovariectomized (OVX) and ovariectomized estradiol-implanted (OVX-E2) rats. In addition, we examined the effects of suppression of serum PRL. Pulsatile injections of GnRH (10-250 ng/pulse) given every 30 min for 24 or 48 h did not increase GnRH-R in OVX or OVX-E2 rats compared to that in saline controls (246 +/- 27 fmol/mg). Bromocriptine treatment (2 mg/day) had no effect on GnRH-R in OVX animals. In contrast, OVX-E2 rats treated with bromocriptine showed significantly increased GnRH-R (500 +/- 43 fmol/mg) in response to GnRH injections. When ovine PRL was administered to bromocriptine-treated OVX-E2 rats, the GnRH induced rise in GnRH-R was abolished. Gonadotropin responses to GnRH were not correlated with changes in GnRH-R. In OVX animals, LH was only elevated in response to 250-ng pulses of GnRH. In OVX-E2 animals, basal LH was increased by all doses of GnRH, and acute responses to 50- and 250-ng pulses were observed. Bromocriptine treatment resulted in increased LH sensitivity to GnRH in OVX rats, but did not further enhance the responses in OVX-E2 animals. We conclude that in female rats, the presence of both E2 and a low serum PRL level is necessary for GnRH to increase GnRH-R, and the interaction of these factors may be involved in the regulation of GnRH-R during the estrous cycle.

Application of the 2-deoxy-(1-14C) glucose method to the study of suprachiasmatic nucleus activity and functions: phasic luteinizing hormone secretion and serotonin innervation.

A semi-quantitative analysis of 2-deoxy-(1-14C) glucose (2 DG) incorporation in the suprachiasmatic nucleus (SCN) was performed in male, castrated female, and castrated oestradiol treated female rats (OVX-E2) during the light period (from 9.00 h to 18.00 h). Unilateral orbital enucleation was carried out on each group. In males and castrated females the 2 DG incorporation in the rostral and caudal SCN was constant throughout the studied period. On the contrary, in OVX-E2 rats, which display a clear cut circadian rhythm of LH secretion, the 2 DG incorporation in the rostral SCN was higher in the afternoon than in the morning. After serotonin (5 HT) depletion, the level of morning labelling reached that of the afternoon. These results suggest the existence of a steroid-linked rhythm of SCN metabolic activity during the light period which might be related to the LH surge and dependent on 5 HT innervation.