Effects of ovarian steroid hormones and thyroxine on calcitonin secretion in pregnant rats

Abstract

In the present study, the roles of ovarian steroid hormones and thyroxine (T4) in regulating the secretion of calcitonin (CT) in pregnant rats were examined. The levels of plasma progesterone, pre- and post-CaCl2plasma CT, and recovery time of plasma CT and calcium after calcium challenge were greatest in midterm pregnant rats. The levels of basal plasma progesterone, CT, calcium, and recovery time of plasma CT after calcium challenge were less in late pregnant rats, but basal plasma estradiol was highest in late pregnancy. The concentrations of plasma T4 were gradually decreased in rats during pregnancy. Regardless of the presence of estradiol, administration of progesterone in ovariectomized (Ovx) rats resulted in an increase of plasma T4 as well as the basal and calcium-induced secretion of CT. Administration of estradiol alone did not alter the CaCl2-induced levels but decreased the post-CaCl2 levels of plasma calcium in Ovx rats. The basal levels of plasma CT were decreased in Ovx rats treated with T4. These results suggest that the hypercalcitoninemia in midterm pregnant rats is due to an increased secretion of progesterone. Hypocalcitoninemia in late pregnant rats, however, is due in part to lower plasma calcium.

The anorectic effect of oestradiol does not involve changes in plasma and cerebrospinal fluid leptin concentrations in the rat

“…Our results showed that, in intact rats, the anorectic effects of oestradiol were evident for 3 days, but from this time onwards they become less potent until they disappeared, which suggest a desensitization process. The 3-day period of time before the initiation of the suggested desensitization would allow oestradiol to exert its anorectic effect to the full during the physiological increases in the hormone -that is, during the 10-12 h of pro-oestrus in every oestrus cycle (Ter Haar 1972, Butcher et al 1974, Wade 1976) and during the last day of pregnancy (Lu et al 1998). It seems reasonable to argue that those anorectic episodes could be beneficial either for mating or for labour respectively, as they release the female from the constrains of searching for food during those periods of time.…”

Effects of estradiol on corticosterone secretion in ovariectomized rats

“…The concentration of plasma E 2 was determined by RIA as previously described, using antiestradiol serum W-1 [Lu et al, 1998]. The sensitivity of E 2 RIA was 1 pg per assay tube.…”

The cyclic AMP-dependent protein kinase A pathway is involved in progesterone effects on calcitonin secretion from TT cells

“…Both estradiol and progesterone have been shown to cause an increase of in vitro CT release from the thyroid C cells of 8-day-old rats (Greenberg et al, 1986). Treatment of ovariectomized rats with progesterone results in an increase of basal and calcium-induced secretion of plasma CT (Lu et al, 1998). Therefore, the secretion of CT from the thyroid gland might be regulated by progesterone in humans; however, the mechanism of progesterone's effects on CT secretion is not clear.…”