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Biomedical subjects

J A Ramaley

Publications and source records attributed to J A Ramaley.

At least 37 records · Page 2Linked to original sources
PubMed1978

The development of the serum corticosterone rhythm in rats.

The purpose of this study was to determine whether the sequence of changes that occur in the adrenal rhythm in maturing female rats (development of a peak, shift in acrophase and amplitude) requires experience with a photoperiodic stimulus or a change in ovarian status. The emergence of the serum corticosterone (CS) rhythm occured more quickly in adult rats placed in a 14 h light, 10 h dark (14:10) cycle at 50 days of age after rearing in constant light (LL) than in weanling rats placed in 14:10. Ovariectomy at weaning age did not alter the pattern of CS development in 14:10 although the amplitude of the peak was reduced even in 25-day-old rats. Adult rats reared in 14:10 held a population rhythm of CS longer after they were placed in LL than did weanling rats placed in LL. This difference was not dependent upon the presence of the ovaries since acutely and chronically ovariectomized (OVX) adult rats responded in a similar manner to adult controls. It can be concluded that the adrenal rhythm emerges as a function of age rather than as a result of a change in ovarian status. The capacity to synchronize serum CS to light-dark cycles develops in the absence of photoperiodic cues.

Age Factors↗
PubMed1976

Effects of ovariectomy on dexamethasone suppression of the adrenal axis in adult rats.

Three weeks after ovariectomy, adult female rats had lower basal levels of serum corticosterone (B), which did not display a daily rhythm, and reduced responses to ether stress, measured by blood levels of B 15 min after ether exposure. Ovariectomized (OVX) females were more sensitive to dexamethasone (DEX) suppression of the ether induced stress response, reaching basal levels at a dose of 50 mug DEX/100 g b.w. At this dose, B levels were reduced by only 30% over saline-control values in intact rats. DEX-treated intact rats displayed a short-term suppression, reaching a maximum 2 h after the injection followed by a rebound 7 h post-injection and a second suppression period evident by 11 h post-injection. OVX rats showed a steadily increasing suppression that began 1 h after injection and persisted to the last sample time at 11 h post-injection. The disappearance of DEX from peripheral blood was followed by means of radioimmunoassay and no difference was found between intact and OVX rats either in the basal state or 15 min after ether stress. It can be concluded that ovarian steroids condition the sensitivity of the adrenal axis to DEX suppression and that the differences in DEX sensitivity we have previously noted between prepubertal and adult rats can be accounted for by a change in gonadal status rather than by a critical developmental event in the adrenal axis itself.

Adrenal Glands↗
PubMed1976

Entrainment of the adrenal rhythm to photoperiod prior to puberty: effects of early experience on the adrenal rhythm and puberty.

The purpose of this study was to determine whether exposure to a cycle of light and dark before the onset of the adrenal rhythm would be necessary in order for rats to develop a normal rhythm of peripheral corticosterone when placed in a test photoperiod at weaning age. Rats were reared in constant light (LL) until weaning age, at which time they were placed in a cycle of 14 h light, 10 h dark (14:10). Females born and reared in 14:10 had peak corticosterone values at 14.00 h on days 22 and 26, and at 18.00 h on days 32 and 36. Males did not display a clear-cut rhythm at 22 or 26 days but had peak corticosterone at 18.00 h on days 32 and 36. Males and females reared in LL until weaning had no rhythm as a group in 14:10 at 24 days of age, but had a corticosterone peak at 18.00 h on days 28 and 40. Females born and reared in LL and exposed to 14:10 for 1 day developed an adrenal rhythm regardless of the age at exposure, but only 25 day old animals showed a normal pattern for their age group. Puberty was advanced in rats exposed to a single day of 14:10 at 25 days of age, but was delayed in younger rats (22 days old), and was unaffected by light exposure in older rats (28 days of age). It can be concluded that early exposure to light-dark cycles is not required for the normal development of an adrenal rhythm in the weanling rat, and that the setting of the corticosterone rhythm to the photoperiod can occur quite rapidly. Rats at 25-26 days of age are able to respond differently to a light cycle challenge than younger rats. A photoperiodic stimulus at that time can advance the onset of puberty.

Adrenal Glands↗
PubMed1976

Serum corticosterone in rats with delayed anovulation.

The purpose of this study was to investigate adrenal function in rats during the development of persistent oestrus to determine whether a change in blood levels of corticosterone would precede or coincide with the onset of infertility. The syndrome of delayed persistent oestrus and anovulation was induced by administration of a low dose (10 mug) of testosterone propionate (TP) at 5 days of age. Control animals were handled without injection or received the vehicle (sesame oil) only. Half of each group was ovariectomized at weaning and received Silastic implants of either oestradiol benzoate (OB) or cholesterol, 3 mm tube length/100 g body weight. Intact rats given the low TP dose showed precocious vaginal opening (27.3 +/- 2.1 days v. 37.6 +/- 2.4 (S.E.M.) days in unhandled controls) and ovulated within 2 days. Persistent vaginal cornification developed in 22 out of 26 rats by 75 days of age. The TP-treated rats had higher corticosterone values than the controls and did not show a further increase after OB implantation. Cholesterol implantation depressed corticosterone levels in the TP-treated rats. The effects of the low TP dose were not dependent upon gonadal function since they persisted in ovariectomized rats. The results suggest that early exposure to androgen can modify the sensitivity of the adrenal system to oestrogen, and can also lead to persistently high values of corticosterone which are not depressed by ovariectomy. These changes precede the onset of persistent oestrus.

Adrenal Glands↗
PubMed1975

Effects of early handling upon puberty: correlations with adrenal stress responsiveness.

Handling of rat pups for 5 min once a week prior to weaning to permit weighing of the litter significantly delays vaginal opening and ovulation and is associated with a reduction in the response to an ether stress administered at 60 days of age. Handling combined with replacement of the bedding material results in a further delay in puberty and a further reduction in the stress response. It is therefore necessary to follow uniform handling procedures in any study of a developmental process.

Adaptation, Physiological↗
PubMed1975

Development of running activity in maturing rats: dependence upon prior androgen exposure and ovarian function.

Female Sprague-Dawley derived rats were given either 1 mg testosterone propionate or an oil vehicle at 2 days of age. At weaning age half of each group were ovariectomized and at puberty the rats were placed in Wahmann activity wheels. In all groups there was a rise in running activity during the first 10 days after vaginal opening. This rise continued progressively in intact, ovulatory rats but did not continue in either persistent estrous or ovariectomized females. Beginning at 85 days of age running activity began to decline in all groups except the ovulatory females. This regression was protected against to some extent by ovariectomy in the androgen-treated females. It can be concluded that the ovaries are not required for either the initiation of running activity or the later decline seen in mature rats but that the gradually increasing running seen in intact rats is directly related to ovarian function.

Adrenal Glands↗
PubMed1975

Effects of dexamethasone before and after puberty on the daily corticosterone rhythm.

Female Sprague-Dawley-derived rats were injected at 25 days of age (prepubertal) or 60 days of age (adult) with 1 mug dexamethasone/100 g b.w. either before the beginning of the daily rise in serum corticosterone (at 10.00 or 12.00 h in adults and 10.00 h in prepubertal rats) or after the daily rise had begun (at 14.00 h in adults, and 12.00 or 14.00 h in perpubertal rats). Blood samples were collected by decapitation at 16.00, 20.00 and 24.00 h on that day and 04.00, 08.00 and 16.00 h the following day. In adults, dexamethasone (DEX) given at 10.00 shifted the corticosterone (B) peak to 04.00. In prepubertal rats, DEX given before the B rise did not shift the subsequent peak and the patterns of B did not diverge from controls. DEX given at 12.00 or 14.00 shifted the peak to 24.00 h. At 08.00 the next day, B was depressed in adults but normal in prepubertal rats. At 16.00 h, both age groups showed depressed B in comparison to controls. Prepubertal rats appear to respond differently to dexamethasone than do adults.

Animals↗
PubMed1975

Rhythms of progesterone and corticosterone in the pms-treated rat: relationship to ovulation.

Precocious ovulation was induced in 26-day-old rats by means of 25 IU pregnant mare's serum gonadotrophin (PMS). Rats were given injections at either 09.00 or 16.00 in order to determine whether the course of pubertal changes in corticosterone (B), progesterone (P) or time of ovulation would be dependent upon the time of injection. Blood samples were collected by decapitation at 4-h intervals on the day of expected ovulation (day 28). In saline-treated controls at 28 days of age there was a demonstrable daily variation in both serum B and P with maximum values at 16.00 and minimum values at 08.00. In rats given PMS at 09.00, there was a peak of P and B at 16.00 on day 28 but the values were higher than in controls. Ovulation took place at 24.00 on day 28-29. In rats given PMS at 16.00 the pattern of P and B was different, with continual high values from 16.00 to 04.00 at 28 days of age; ovulation took place later in this group (between 02.00-08.00 on day 28). It can be concluded that there is a daily rhythm of P a few days before puberty and that the induction of precocious ovulation with PMS is associated with a different pattern of B and P and a different time of ovulation depending upon when PMS is administered.

Adrenal Glands↗