Biomedical subjects

M H Morehead

Publications and source records attributed to M H Morehead.

4 recordsLinked to original sources

PubMed1990

Stress-induced suppression of the prolactin afternoon surge in ovariectomized, estrogen-treated rats and the nocturnal surge in pseudopregnant rats are accompanied by an increase in median eminence dihydroxyphenylacetic acid concentrations.

Experiments were performed to determine whether the suppression of prolactin (PRL) surges during restraint was accompanied by changes in the activity of tuberoinfundibular dopamine (TIDA) neurons in the median eminence. Animals were either ovariectomized and estrogen-treated (OVX-PEP) or cervically stimulated to induce pseudopregnancy (PSP). Restraint stress was administered by tying the hind legs together with plastic-coated bell wire. Animals were decapitated following 15 or 30 min of restraint stress or immediately after removal from the animal room (control) when PRL levels were basal (10.00 h), at the peak of the afternoon PRL surge in OVX-PEP animals (17.00 h) or the nocturnal PRL surge in PSP animals (05.00 h). Median eminence dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were significantly decreased in control rats at 17.00 h when compared to control rats at 10.00 h (103.1 +/- 3.7 vs. 85.8 +/- 3.3 and 11.4 vs. 7.1 +/- 0.4 pg/micrograms protein, respectively) and plasma PRL was markedly elevated. Restraint stress at 10.00 h resulted in a significant increase in serum PRL, but this increase was not accompanied by a change in DA or DOPAC when compared to control animals (103.1 +/- 3.7 vs. 107.9 +/- 4.8 and 11.4 +/- 0.4 vs. 10.4 +/- 0.6 pg/micrograms protein, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗

PubMed1989

The restraint stress-induced decrease of the nocturnal prolactin surge and the physiology of pseudopregnancy and pregnancy in the rat.

Experiments were performed to determine whether the restraint stress-induced decrease of the nocturnal prolactin (PRL) surge affected the length of pseudopregnancy (PSP) and/or the outcome of pregnancy in rats. Vaginal cycles were monitored daily and animals were electro-mechanically cervically stimulated on the morning of metestrus to induce PSP. Animals were restraint stressed by tying the hind legs together with plastic coated bell wire beginning on day 1 of PSP from 0100-0700h with reapplication of stress at 0400h for 6-9 days and then blood sampled for PRL and progesterone plasma levels. Restraint stress significantly decreased plasma PRL (P less than 0.001) and progesterone (P less than 0.05) levels. The length of PSP was significantly decreased (P less than 0.01) for restraint animals and for control animals that were blood sampled compared to control animals that were not sampled. In the pregnancy experiment, animals were mated upon arrival into the laboratory and assigned to one of four groups. For the restraint group, stress was initiated on day 1 of pregnancy as indicated by the presence of sperm in the vaginal lavage. Animals were stressed for 6-9 days for 6 hours during the nocturnal PRL surge as described above. One control group had no treatment; a second control group was sampled only, and a third control group was injected daily with pimozide, a dopamine antagonist, and stressed for 6-9 days. The group which received no treatment had significantly greater (P less than 0.05) incidence of successful pregnancy compared to the other 3 groups; there were no differences (P greater than 0.05) between the sampled, restraint and restraint + pimozide groups in the incidence of successful pregnancy. We conclude that restraint stress during the nocturnal PRL surge minimally affects the length of PSP and that the effect of stress on the outcome of pregnancy is not due to the decrease in nocturnal PRL surge.

Animals↗

PubMed1987

The lack of a physiologic effect of the stress-induced decrease of the proestrous prolactin surge in the rat.

Experiments were performed to determine whether the restraint stress-induced decrease in the proestrous prolactin (PRL) surge blocked luteolysis of the corpora lutea (CL), affected ovulation, or prevented the induction of pregnancy/pseudopregnancy in the next cycle. In all experiments rats were either stressed on proestrus and estrus, administered daily sc injections of 1 mg/day of 2-Br-alpha-ergocryptine (CB-154) for 4 days starting on diestrus II or not treated. In one experiment animals were sampled on the afternoon of proestrus to determine the effect of restraint stress on plasma PRL values and sacrificed on the morning of proestrus in the next cycle. Ovaries were removed, weighed, fixed and examined for number of CL. Restraint stress resulted in a significant increase in ovarian weight when compared to controls; CB-154 resulted in significant increases in ovarian weight when compared to stress and control animals. However, only CB-154-treated animals had a significant increase in the number of CL when compared to controls. In another experiment, animals were sacrificed on estrus of the next cycle and the oviducts examined for the number of ova. There were no differences among groups. In the final experiment, animals were placed with males of proven fertility on proestrus of the next cycle and examined for evidence of sperm in the vaginal lavage and/or vaginal plugs. CB-154 prevented the induction of pregnancy or pseudopregnancy due to a carry over effect of the drug on PRL surges. Restraint stress had no significant effect on the induction of pregnancy or pseudopregnancy. We conclude that there is no physiological significance to the stress-induced decrease of the proestrous PRL surge with respect to ovarian function or fertility.

Animals↗

PubMed1987

Restraint stress depresses prolactin surges in pseudopregnant rats and adrenalectomy does not alter the response.

Experiments were performed to determine whether restraint stress decreases the two prolactin (PRL) surges in pseudopregnant (PSP) rats in a manner similar to the stress-induced decrease of the proestrous PRL surge. Adrenal involvement as well as adaptation of the response was also investigated. Vaginal cycles were followed and animals exhibiting 2-3 normal cycles were cervically stimulated (CS) electromechanically to induce PSP. In one experiment the effect of adrenalectomy (ADX) on the nocturnal surge (NS) was investigated and was found to have no effect. In another set of experiments the effect of restraint stress was investigated. Immediately following an initial sample, the animals to be stressed had their hind legs tied together with plastic coated bell wire. Subsequent samples were taken for 3 hours. Restraint stress decreased the NS to 15% of the initial value within 30 minutes. ADX did not alter this response. Furthermore, 6-9 days of 3 hours of restraint stress did not attenuate the stress-induced decrease of the NS. Restraint stress also depressed the diurnal surge in PSP rats. These results indicate that restraint stress applied during the two PRL surges of PSP results in significant decreases in plasma PRL and that this response is not altered by ADX or by habituation to the stimulus.

Adrenalectomy↗