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Biomedical subjects

J D Dunn

Publications and source records attributed to J D Dunn.

At least 73 records · Page 4Linked to original sources
PubMed1978

Ethanol-increased exhalation of mercury in mice.

CBA/J mice injected three days beforehand with 203HgCl2 were given ethanol or water by gavage and placed in a chamber designed to collect exhaled mercury. Ethanol treatment led to an eight-fold increase of counts accumulated on a filter over a four-hour period, compared with water-treated mice. The mercury-collection apparatus tested for extracorporeal contribution of volatilised mercury indicated that the counts originated from the air exhaled by the mice.

Animals↗
PubMed1978

Effect of adrenalectomy on temporal patterns of serum gonadotropin levels.

To determine whether adrenocortical function influences rhythmic gonadotropin patterns in male rats, blood samples were obtained by rapid decapitation from control and adrenalectomized male rats at 3-h intervals over a 24-h period (14 h light/day, 4 a.m.--6 p.m.). Control animals showed periodicity in serum LH, prolactin (Prl) and corticosterone similar to that reported previously. Peak and trough serum levels of corticosterone and Prl occurred at 5 p.m. and 8 a.m. respectively whereas those for LH occurred at 11 p.m. and 11 a.m. Serum FSH levels did not vary with circadian periodicity. 15 days after adrenalectomy, serum LH levels continued to fluctuate with a circadian periodicity but showed a marked phase shift; peak LH levels were observed at 8 a.m. The absence of adrenal hormones did not result in altered FSH levels nor was the phase of the Prl rhythm significantly altered.

Adrenal Cortex↗
PubMed1978

Pentobarbital anesthesia: interference in the effects of other pharmacological agents and of electrical stimulation on prolactin secretion.

In adult male rats, a pretreatment regimen of serial injections of dexamethasone (1 mg/kg), morphine (20 mg/kg) and pentobarbital (40 mg/kg) was evaluated for use in conjunction with studies on the effects of hypothalamic electrical stimulation on prolactin secretion. Serum prolactin levels were measured before and 15 min after electrical and sham stimulation of the hypothalamic arcuate nucleus in rats subjected to either the pharmacological regimen or to pentobarbital anesthesia alone. Pentobarbital alone caused a transient rise in serum prolactin levels, which obscured any effect of electrical or sham stimulation; this interference was not overcome by the addition of dexamethasone and morphine treatment. Thus, the result indicate that the acute stimulatory affect of pentobarbital anesthesia on prolactin release may interfere with further manipulation of prolactin-controlling mechanisms, by either pharmacological or surgical means. Furthermore, the dexamethasone-morphine-pentobarbital pretreated rat does not provide an adequate preparation for studing the effects of electrical stimulation on prolactin secretion.

Anesthesia↗
PubMed1978

Circadian variation in the sensitivity of the pituitary-adrenal system to dexamethasone suppression.

Intact female rats were injected with 100 microgram dexamethasone/kg body weight or saline at 12.00, 24.00 or 04.00 h. Four hours later, i.e. 16.00, 04.00 or 08.00 h respectively, a double bleeding procedure was used to obtain blood samples from stressed and unstressed rats for subsequent fluorometric determination of corticosterone levels in the plasma. The difference between the level of corticosterone is stressed and unstressed rats (the stress increment) was determined and used as an index of the response of corticosterone in the plasma to stress. Increments in the levels of corticosterone in the plasma evoked by stress in rats injected at 12.00 h with dexamethasone and bled 4 h later were significantly (P less than 0.05) less than those in rats given dexamethasone at 24.00 or 04.00 and bled at 04.00 or 08.00 h respectively. In contrast, stress-induced increments in the level of corticosterone in the plasma of rats treated with saline did not vary with the time of day.

Animals↗
PubMed1977

Circadian variation in plasma melanocyte stimulating hormone activity in the rat.

Non--stress levels of plasma melanocyte stimulating hormone (MSH) and corticosterone were determined at 3-h intervals during controlled light--dark cycles in adult, male rats. Significant 24-h periodicity was demonstrated for both plasma MSH and corticosterone. Whereas plasma MSH values were not as high during the early evening hours as during the early morning hours, plasma corticosterone levels showed a marked rise during the early afternoon and crest values occurred just before the lights off phase of the 24-h light--dark cycle. These results indicate that in the rat, the level of MSH in plasma fluctuates with a low amplitude circadian frequency which is not in phase with that observed for plasma corticosterone.

Adrenocorticotropic Hormone↗
PubMed1976

The effect of surgical isolation or ablation of the medial basal hypothalamus on serum prolactin levels in male rats.

Complete isolation of ablation of the medial basal hypothalamus (MBH) was performed in adult male rats, and non-stress prolactin levels were measured by radioimmunoassay in blood collected by decapitation at 24h, 2 weeks and 6 weeks following surgery. 24 h after surgery, medial hypothalamic ablation (MHA) markedly elevated prolactin levels compared to those of intact control rats; prolactin levels subsequently declined to normal resting values 2 to 6 weeks following surgery. Circulating prolactin levels following hypothalamic isolation were not different from those of controls at either acute or chronic sampling intervals. These data suggest that chronic isolation or destruction of the MBH does not alter basal prolactin secretion in male rats, provided that circadian and stress-induced variations in control animals are properly considered.

Adrenal Glands↗
PubMed1976

Stress-induced gonadotropin and prolactin secretory patterns.

To further evaluate the influence that sex, time of day and/or stage of the estrous cycle have on stress-induced changes in gonadotropin secretory patterns, rats were subjected to acute ether stress and subsequently sacrificed at 1.5, 3, 5, 10 and 15-min intervals. A significant change in FSH levels was not detectable, however serum LH levels consistently showed a transient elevation, and prolactin release occurred rapidly and in large increments in every case. Variation in basal hormone levels due to sex, circadian rhythmicity, or estrous cyclicity did not alter the pattern of the response of individual hormones to the stress but did markedly influence the magnitude of the response.

Animals↗
PubMed1976

Pituitary-adrenal function in thyroparathyroidectomized male and female rats.

The influence of thyroid hormones on pituitary-adrenal function was assessed by studying several aspects of adrenocortical function approximately 30 days after thyroparathyroidectomy (TPTx). Both male and female rats showed evidence of rhythmic adrenocortical activity; peak plasma corticosterone levels occurred just before the dark phase of the lighting schedule. Only the amplitude of the rhythm appeared altered by TPTx. Peak plasma corticosterone levels in TPTx male and female animals were less (P less than 0.05) than corresponding levels in intact control rats. Both sexes showed significant responses to stress, but the morning stress response in TPTx females was less (P less than 0.01) than the stress response in intact controls. Concomitant with the reduced stress response, the adrenocortical response to exogenous ACTH was reduced in TPTx female rats.

Adrenal Glands↗
PubMed1976

Effect of thyroidectomy on rhythmic gonadotropin release.

Nonstress blood samples were obtained from intact and thyroidectomized (TE) male rats at 3-hr intervals over a 24-hr period via rapid decapitation. The animals were thyroidectomized when 40 days old and used 6 weeks later. Intact animals showed periodicity in serum LH (P less than 0.01) and prolactin (P less than 0.01). Both gonadotropins began increasing after 8 PM and peak levels occurred at 11 PM. In contrast, 24-hr periodicity was not observed in serum FSH. Corticosterone levels in these same serum samples showed the expected circadian periodicity. After TE, the 24-hr pattern in all gonadotropins was altered significantly. Serum LH increased (P less than 0.01) and circadian periodicity appeared to be absent. FSH and prolactin levels were increased and decreased, respectively (P less than 0.01), with serum prolactin showing a 9-hr phase shift. Prolactin began increasing at 2 AM and reached a peak at 8 AM. Corticosterone in TE animals showed a 24-hr rhythm similar to that of intact rats. These findings confirm our previous observations that nonstress serum LH and prolactin levels fluctuate with a 24-hr periodicity and suggest that the level of, and the phase angle betweeen, these rhythms is markedly influenced by pituitary-thyroid activity.

Animals↗