Biomedical subjects

J A Ramaley

Publications and source records attributed to J A Ramaley.

At least 55 records · Page 3Linked to original sources

PubMed1975

Adrenal-gonadal function in rats with frontal hypothalamic transections.

All neural connections entering the hypothalamus from the anterior direction were severed by means of a Halász knife-cut in female rats at 22 days of age. The rats were then examined for vaginal opening and ovulation. At intervals blood samples were collected by cardiac puncture for the measurement of serum corticosterone (B). Unoperated rats showed vaginal opening at 36.5 +/- 2.1 days and ovulation within 2 days. A significant difference was found between B at 08.00 h and 18.00 h at the first sample interval chosen (28 days of age) and thereafter. Animals given sham surgery showed vaginal opening late (44.2 +/- 3.2 days, p smaller than 0.05) but ovulated within 2 days. These animals also had a significant 08.00-18.00 difference in B from day 28 on. Rats with frontal cuts in front of the suprachiasmatic nucleus (SCN) showed precocious vaginal opening (27.2 +/- 2.3 days, p smaller than 0.05) and early ovulation (28.2 +/- 0.7 days). A 08.00-18.00 difference was noted at 28 days of age but was lost after ovariectomy at 47 days of age. Implantation of a silastic estradiol benzoate capsule restored the 08.00-18.00 difference (p smaller than 0.01). Animals with cuts behind the optic chiasm (posterior frontal cuts) all showed early vaginal opening; some rats then ovulated (at 42.3 +/- 3.8 days) while others did not. No difference could be detected in the position of the cuts although there appeared to be more damage to the region just behind the SCN in the latter group. No 08.00-18.00 difference in B was found in the nonovulatory group and no difference was found in the ovulatory group until 44 days of age. It can be concluded that an isolated hypothalamic island containing the SCN will generate signals sufficient for precocious ovulation although subsequent ovulatory cycles are not regular.

Adrenal Glands↗

PubMed1975

The effect of an acute light cycle change on adrenal rhythmicity in prepubertal rats.

24 and 28 day old rats, raised in a 14 h light: 10 h dark (14:10) cycle, showed a clear serum corticosterone (B) peak at the beginning of the dark period (18.00 h) with an amplitude of 25-30 mug%. Other B values during the 24 h period were lower (9-12 mug%). Rats raised in a 8.5:15.5 cycle had a B peak (after onset of the dark period, at 22.00 h). Rats raised in constant light (LL) showed no variation in B throughout the 24 h. Weanling rats raised in a 8.5:15.5 cycle appeared to synchronize more rapidly to a 14:10 cycle than did rats raised in LL. When placed in LL at weaning, rats raised either in 14:10 or 8.5:15.5 had lost their periodicity by day 24. When rats raised in 8.5:15.5 were shifted to LL or 14:10 after weaning age (day 24), the pattern of response was different. One day after the shift, rats placed in a 14:10 cycle displayed a pattern of B synchronized to the normal 14:10 pattern for rats born and raised in that light cycle. This synchrony persisted for at least 3 days. Rats placed in 14:10 at 21 days of age did not show a fully synchronized pattern until day 28. It can be concluded that weanling rats exposed to a light-dark cycle adapt quickly to a new light cycle and that older prepubertal rats shift even more quickly.

Adaptation, Physiological↗

PubMed1975

Precocious puberty: the effect of adrenalectomy on PMS-induced ovulation and progesterone secretion.

Female Sprague-Dawley derived rats were received at 21 days of age and either sham-operated or adrenalectomized on that day. Half of the animals received either 25 IU pregnant mare's serum gonadotrophin (PMS) or 0.9 saline at 9 AM on the next day; the other half were injected at 26 days of age. On the day of expected ovulation (days 24-25 and days 28-29) the rats were killed at 4-hr intervals and the incidence of ovulation determined. Serum progesterone and corticosterone were measured with the intent of comparing the pattern of these steroids with the timing and incidence of ovulation. Twenty-two-day-old rats given PMS ovulated later (at 0400 on day 25) than did the 26-day-old rats (at 2400 on day 28). Adrenalectomized ADRX rats ovulated later than intact controls at both ages (ovulation complete at 1600 on days 25 and 29, respectively). There was a reduced ovarian weight response to PMS in ADRX rats but uterine weights were not consistently different from intact PMS-treated rats. Associated with the different timing of ovulation and organ weight response in the ADRX rats there was a lower serum progesterone response on days 24-25. In intact PMS-treated rats, the rhythm of the serum corticosterone was different in the two age groups. It is concluded that adrenalectomy alters the normal response to PMS resulting in a delay in the time of ovulation. It is possible that the adrenal normally participates in the induction of ovulation after PMS, possibly by acting as an internal priming agent to facilitate gonadotrophin release in the young rat.

Adrenal Glands↗

PubMed1975

Differences in serum corticosterone patterns in individual rats: relationship to ovulatory cycles.

Blood samples were collected on several occasions from Sprague-Dawley-derived rats by means of cardiac puncture at 8 h intervals over a 24 h period. Rats were sampled four times before ovariectomy, after ovariectomy and after replacement therapy with oestradiol benzoate. It was discovered that each rat tended to maintain a distinct pattern of serum corticosterone. While some rats developed hormonal rhythms, other rats showed no evidence of such rhythms as indicated by patterns of serum corticosterone concentation. The majority of rats that did not show daily corticosterone rhythms were found to have irregular ovulatory cycles as indicated by vaginal smears. Each characteristic hormonal pattern remained after ovariectomy and subsequent oestrogen replacement although resting levels of corticosterone were lower after ovariectomy and higher after oestrogen treatment than before the operation. It is concluded that the presence of an adrenal rhythm is usually associated with regular vaginal smear cycles.

Animals↗

PubMed1975

Adrenal rhythmicity in the immature pseudopregnant rat.

A daily rhythm of serum corticosterone persists in 31 day old immature female rats in which pseudopregnancy has been induced by means of 25 IU pregnant mare's serum gonadotrophin (PMS) given at 26 days of age. There is, in addition, a daily rhythm of progesterone in 31-day old controls with a rise during the day and a fall during the dark portion of the photoperiod. PMS-injected rats had a much higher level of progesterone but no rhythm.

Adrenal Glands↗

PubMed1974