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Biomedical subjects

G D Riegle

Publications and source records attributed to G D Riegle.

At least 37 records · Page 2Linked to original sources
PubMed1981

Sexual differences in tuberoinfundibular dopamine nerve activity induced by neonatal androgen exposure.

The activities of different catecholaminergic neurons in the brains of male amd female rats were estimated by measuring (1) the rate of decline of dopamine (DA) and norepinephrine (NE) after inhibition of tyrosine hydroxylase with alpha-methyltyrosine (alpha-MT) and (2) the rate of accumulation of dihydroxyphenylalanine (DOPA) after inhibition of DOPA decarboxylase with NSD 1015 in brain regions containing the terminals of these neurons. In the median eminence the accumulation of DOPA and the alpha-MT-induced decline of DA, but not NE, were higher in the female than in the male, suggesting increased activity of tuberoinfundibular DA neurons in the female. There were no sexual differences in DA neurons which terminate in any of the other brain regions (striatum, olfactory tubercle, nucleus accumbens, posterior pituitary). To determine if the sexual difference in tuberoinfundibular DA neuronal activity results from neonatal exposure to androgens, the rate of DOPA accumulation was examined in the median eminence of females, males, and androgen-sterilized females (all of which were castrated as adults) and in adult males which were castrated as neonates. Similar values for DOPA accumulation were observed in the median eminence of castrate females and neonatally castrated males, while significantly lower values were observed in castrate males and androgen-sterilized females. Thus, neonatal exposure to androgens alters the activity of tuberoinfundibular DA neurons. Neonatal androgen-induced differences in tuberoinfundibular DA neuronal activity may be responsible, in part, for sexual differences in the hypothalamic regulation of hypophyseal hormone secretion.

Aging↗
PubMed1980

Characteristics of dopaminergic neurons in the aged male rat.

Male rats were sacrificed at 5 months (young rats) or at 24 months (aged rats). When compared with values in young rats, aged rats had higher serum concentrations of prolactin and lower concentrations of luteinizing hormone and testosterone. In the median eminence, which contains the terminals of tuberoinfundibular dopamine (DA) neurons, the concentrations of DA and dihydroxyphenylactic acid (DOPAC), and the rate of DA synthesis (accumulation of DOPA after the inhibition of DOPA decarboxylase) were decreased in aged rats. In the striatum, which contains the terminals of nigrostriatal DA neurons, the concentration of DA was reduced, but this change was not accompanied by a decrease in DOPAC concentrations or DOPA accumulation. The decreased DA concentration observed in the median eminence and striatum of aged rats may reflect the loss of DA neurons. An attempt was made to mimic the age-related loss of nigrostriatal and tuberoinfundibular DA neurons by pretreating rats with intraventricular injections of 6-hydroxydopamine. In these animals the decrease of DA in the median eminence was accompanied by a concomitant reduction in the rate of DOPA accumulation, whereas in the striatum the concentration of DA was reduced, but DOPA accumulation remained normal. These results suggest that in aged and 6-hydroxydopamine-treated rats, the loss of nigrostriatal DA neurons is accommodated for by a compensatory increase in the activity of the remaining neurons whereas tuberoinfundibular DA neurons are unable to compensate in a similar manner.

Aging↗
PubMed1979

The effect of age on reproduction in repeatedly mated female rats.

The effects of age and repeated pregnancies on reproduction were studied in Long-Evans rats. Indices of reproduction measured included estrous cycles, successful mating, numbers of rats producing litters, average litter size, average pup weight and serum LH-from a 4 pm proestrous blood sample. There were no differences in these reproductive parameters between rats with serial pregnancies initiated at 2 or 9 mo of age. The percentage of rats producing normal litters was reduced much faster than the percentage of successfully mated rats with normal ovarian cycles. Although 60% of the rats still had normal ovarian cycles and were mated at 17 mo of age, only one rat (4%) produced a litter. Increasing age and multiple pregnancies did not significantly affect the LH concentration of the proestrous blood sample or the average litter size or pup weight of the rats with successful pregnancies. These data suggest post-ovulatory loss of reproduction in the aging rat.

Animals↗
PubMed1978

Hypothalamic LH-releasing activity in young and aged intact and gonadectomized rats.

Hypothalamic LH-releasing activity content was measured in young (3-5 mo) and aged (22-26 mo) intact and gonadectomized male and female rats. Hypothalamic extracts (0.25, 0.5 and 1.0 hypothalamus equivalents) from young and aged rats were incubated with untreated hemisectioned rat pituitaries in medium 199. All hypothalamic extract treatments stimulated LH release from the incubated pituitaries. Increased amounts of hypothalamic extracts added to to the incubation medium proportionally increased LH release. There were no differences in LH release stimulated by young or aged hypothalamic extracts from either the intact or gonadectomized groups. In addition serum testosterone concentrations were reduced in the aged male rats and serum LH was lower in aged male and female rats than in the young groups. Although serum LH was increased after gonadectomy in all groups, the increase was of smaller magnitude in the aged rats. These data indicate significant alterations in the responsiveness of the hypothalamus to steroid feedback in the aged rat. Although the hypothalamus contains sufficient LH-releasing activity to stimulate higher levels of pituitary and gonadal endocrine function, aging effects on the neuroendocrine control mechanisms inhibit hypothalamic hormone function.

Aging↗
PubMed1978

Serum testosterone and testicular response to HCG in young and aged male rats.

Serum testosterone and testicular response to HCG was measured in young (3 - 6 mo) and aged (20 - 30 mo) male Long-Evans rats. Serum testosterone was measured by radioimmunoassays on serial blood samples taken before and after injections of HCG. Control group serum testosterone concentrations were lower in aged compared to young groups. Intravenous injection of 1, 5, and 20 IU of HCG increased serum testosterone in both age groups and testosterone remained elevated throughout the 150-min sampling interval. The increase in serum testosterone concentrations following acute HCG stimulation was greater in young than in aged rats. Serum testosterone concentrations and testicular response to intravenous HCG injections were increased to similar levels in young and aged male rats following 7 days of daily subcutaneous injections of 5 IU of HCG/100 gm bw. These data suggest that while testicular secretion and responsiveness is reduced with age, the aged male rat retains the capacity to secrete more testosterone than it normally maintains.

Aging↗
PubMed1977

Thermorespiratory responses of shorn and unshorn sheep to mild heat stress.

Three 3-year-old ewes with surgically exteriorized carotid loops were twice exposed to ambient temperatures (Ta) of 25, 30, 35 and 40 C (at constant 40% relative humidity) for 120 min in the presence (6.6 cm) and absence (less than 0.3 cm) of fleece. Thermoregulatory responses were evaluated during the last 30 min of each exposure by measurements of rectal (Tre), 6 skin surface temperatures (Ts), respiratory frequency (f), oxygen consumption (Vo2) and respiratory evaporative heat (Er); arterial blood samples were analyzed for pH, Pco2 and HCO-3 concentration. Both shorn and unshorn sheep exhibited a progressive increase in f, Er and Ts as Ta was elevated, with the unshorn group showing a higher Er than the shorn sheep at each Ta without a significant change in heat production. Er was found to be the principal avenue of heat loss, accounting for as much as 59% of the total in the shorn sheep compared to65% for the unshorn sheep. Increases in Er were accompanied by a decline in the arterial Pco2 which was linearly related to the Ta in both shorn and unshorn sheep. These data suggest that in defending against hyperthermia, sheep appear unable to increase Er without a concurrent elevation in Va at nearly allstages of acute heat stress.

Animals↗
PubMed1977

Effect of aging on hypothalamic LH-releasing and prolactin inhibiting activities and pituitary responsiveness to LHRH in the male laboratory rat.

Hypothalamic content of LH releasing and prolactin inhibiting activities and pituitary responsiveness to LH releasing hormone was measured in young (4 mo.) and aged (26 mo.) Long-Evans rats by in vitro methods. Hypothalamic extracts (0.5 and 1.0 hypothalamic equivalents) from young and aged male rats were incubated with untreated hemisected rat pituitaries in medium 199. Doses of 0.5 and 1.0 hypothalamic equivalents (HE) from both age group stimulated LH secretion. The increase in pituitary LH release stimulated by 0.5 HE from aged male rats was about half that stimulated by 0.5 HE from the young male group (p less than .20). The increase in LH secretion stimulated by hypothalamic extracts of either age group was not associated with a change in pituitary LH content. Although 0.5 and 1.0 HE from young male rats and 1.0 HE from the aged group reduced incubated pituitary prolactin release, 0.5 HE from the aged males did not affect prolactin release. Treatment with hypothalamic extracts also resulted in increased pituitary prolactin concentrations. Pituitaries from young and aged male rats were incubated in medium 199 containing 0, 25, or 100 ng of LH releasing hormone. Although LH releasing hormone stimulated LH secretion in all groups, the increase in release of LH was less in the aged groups than from pituitaries from the young male rats. Pituitary LH content of the aged male group was only about 1/4 that of the young group.

Aging↗
PubMed1977

Effects of electroanesthesia and a phenothiazine tranquilizer on thermoregulation in the sheep.

The effects of giving propiopromazine alone and of electroanesthesia-propiopromazine treatment on thermoregulation (body temperature regulation) were studied in 3 sheep at ambient temperatures of 5, 25, and 35 C. Measures of thermoregulation during a 120-minute treatment and 120-treatment recovery period included rectal temperature, respiratory frequency, respiratory evaporative heat loss, metabolic heat production, multiple skin temperatures, and shivering. During cold exposure (5 C), both the propiopromazine administration and the electroanesthesia-propiopromazine treatment resulted in hypothermia which was attributed to increased peripheral and respiratory heat losses, a transient inhibition of shivering thermogenesis, and a reduction in metabolic heat production. At 35 C ambient temperature, both resulted in hyperthermia caused principally by a reduction in respiratory evaporative heat loss. The effects of electroanesthesia-propiopromazine treatment on thermoregulation appeared to be additive at both the cold (5 C) and the hot (35 C) environments, in that simultaneous administration resulted in a more profound thermoregulatory impairment. Nevertheless, shifts in body temperature during electroanesthesia are partly attributable to phenothiazine premedication.

Animals↗
PubMed1976

Aging effects on hypothalamic dopamine and norepinephrine content in the male rat.

Hypothalamic content of dopamine and norepinephrine was measured in young (4 mo) and aged (24-26 mo) male rats by aluminum oxide adsorption and microfluorescence. Hypothalamic content of both dopamine and norepinephrine was significantly less in aged than in the young groups. Average dopamine content of the young and aged groups was 32.5 +/- 9.3 and 15.6 +/- 2.5 ng/hypothalamus, respectively. Norepinephrine content averaged 47.6 +/- 10.7 and 22.8 +/- 1.8 ng/hypothalamus in the young and aged groups. These data suggested that alterations in hypothalamic catecholamine function contribute to changes in endocrine control mechanisms during aging.

Aging↗
PubMed1976

Effects of aging on LH and prolactin after LHRL L-dopa, methyl-dopa, and stress in male rat.

Hypothalamic-pituitary control of prolactin and LH secretion was tested in young (4-6 months) and aged (22-30 months) male Long-Evans rats given L-dopa, methyl dopa, LHRH, or stress treatments. Pretreatment serum LH levels were consistently higher in young than in the aged groups. The increase in serum LH after LHRH injection was only about half as much in aged as compared to young control males. Although acute stress caused a prompt increase in serum LH in young male rats, this treatment was without effect in the aged group. Methyl dopa treatment stimulated serum prolactin secretion in both young and old rats. Although L-dopa treatment caused a reduction in serum prolactin in both age groups, the sensitivity, magnitude, and duration of the reduction was smaller in the aged rats.

Aging↗