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E J Mock

Publications and source records attributed to E J Mock.

17 recordsLinked to original sources
PubMed1984

Interactions of prostaglandins with subpopulations of ovine luteal cells. II. Inhibitory effects of PGF2 alpha and protection by PGE2.

Purified preparations of ovine large luteal cells were utilized in a series of experiments to test the effects of prostaglandins (PG) E2 and F2 alpha on cell morphology, viability and secretion of progesterone. Luteal cells were allowed to attach to culture dishes overnight before experiments. In the first series of experiments incubation of large steroidogenic cells with PGF2 alpha for 6 hr resulted in morphological changes including a retraction of the cell cytoplasm and apparent extrusion of cytoplasmic components which became more pronounced after 12 hr. In a second series of experiments, PGF2 alpha decreased and PGE2 increased progesterone accumulation in media after 6 hr when media were not replaced during the incubation period, while progesterone accumulation was not different than that observed in control dishes when both prostaglandins were present. Hourly replacement of the media negated the inhibitory effects of PGF2 alpha but had no effect on the stimulated secretion of progesterone induced by PGE2. Finally, in incubations without media replacement, PGF2 alpha induced a dose-dependent decrease in progesterone accumulation while PGE2 elicited a biphasic response with progesterone secretion increasing from 0.1 ng/ml to maximal levels at 10 ng/ml followed by a dose-dependent decrease at 100 and 1000 ng/ml. These data are compatible with the hypotheses that: 1) luteolysis is initiated, at least in part, by an action of PGF2 alpha on large luteal cells; and 2) the embryonic signal from the pregnant uterus which rescues the ovine corpus luteum may be PGE2.

Animals↗
PubMed1984

Hypophysectomy and hemivasectomy can inhibit the testicular hemicastration response of the mature rat.

Three questions were asked in an attempt to understand how testosterone (T) concentration in the veins of the remaining testis can double within 24 h after hemicastration in the mature rat without a change in plasma luteinizing hormone (LH) levels. These three questions (and their answers) were: 1) Can the testicular hemicastration response occur in hypophysectomized rats? Answer, No. 2) Does LH binding to the testis increase after hemicastration? Answer, No. 3) Is there a neural route to the testis alternate to the superior spermatic plexi? Answer, Yes, apparently there is, since hemivasectomy contralateral to the excised testis partially suppressed the testicular hemicastration response (150.4 +/- 13.2 ng/ml in hemicastrated, sham- hemivasectomized rats [n = 18] vs. 109.4 +/- 11.6 ng/ml in hemicastrated, hemivasectomized rats [n = 18], P less than 0.026). It was concluded that LH was probably necessary to the testicular hemicastration response but that its presence did not provide a mechanism. The response was mediated at least partly through the inferior spermatic nerves associated with the vas deferens. A possible reason, although highly speculative, for failure to previously block the testicular hemicastration response by bilateral denervation of the superior spermatic plexi (Mock and Frankel , 1982) was that during the 12-wk interval between denervation and hemicastration, testicular innervation functionally transferred from the superior spermatic to the inferior spermatic nerves.

Animals↗
PubMed1983

Differences in the rates of internalization of 125I-labeled human chorionic gonadotropin, luteinizing hormone, and epidermal growth factor by ovine luteal cells.

The rate of internalization and degradation of radioiodinated hCG, ovine LH (oLH), human LH (hLH), and mouse epidermal growth factor (mEGF) was studied in suspensions of ovine luteal cells. Hormone bound to the plasma membrane was quantified by treating the cells with acidic buffer (pH 3.0), and the radioactivity removed from the receptor was measured. The radioactivity remaining in the cell pellet was considered to have been internalized. The extent of degradation of the radioactive hormones was determined by subjecting the radioactivity that was released into the medium during the incubation periods to precipitation with 20% trichloroacetic acid. The non-precipitable radioactivity was considered to have been degraded. The required time for loss of half of the radioactivity that had been bound to the cell membrane at time zero was 22.8 +/- 2.3 h for hCG, 23.3 +/- 1.1 h for asialo-hCG, 15.1 +/- 1.4 h for hLH, 0.4 +/- 0.2 h for oLH, and 0.3 +/- 0.1 for mEGF. The quantities of radioactivity that had been internalized (intracellular plus degraded) were greater at earlier times (15-120 min) for oLH or mEGF than for hCG, asialo-hCG, or hLH. These data suggest that ligands bound to different receptors on ovine luteal cells are internalized and degraded at different rates by the same cell and that ligands that bind to the same receptor (hCG, hLH, and oLH) can also be internalized and degraded at very different rates.

Animals↗
PubMed1983

Internalization of ovine luteinizing hormone/human chorionic gonadotropin recombinants: differential effects of the alpha- and beta-subunits.

The rate of internalization and degradation of radioiodinated hCG and ovine LH (oLH) as well as homologous and heterologous recombinants of their subunits was studied in suspensions of ovine luteal cells. Hormone bound to the plasma membrane was quantified by treating the cells with acidic buffer (pH 3.0) and quantification of the radioactivity that was removed from receptor. The radioactivity remaining in the cell pellet was considered to be intracellular. The extent of degradation of the radioactive hormones was determined by subjecting the radioactivity released into the medium during incubation to precipitation with 20% trichloroacetic acid. The non-precipitable radioactivity was considered to have been degraded. Radioactivity was lost from the cell membrane with a t1/2 of 16.8 +/- 2.5 h for radioiodinated hCG, 22.8 +/- 3.8 h for the alpha-subunit of hCG recombined with radioiodinated beta-subunit of hCG, 8.9 +/- 4.5 h for the alpha-subunit of oLH recombined with the radioiodinated beta-subunit of hCG, 0.5 +/- 0.1 h for the alpha-subunit of hCG recombined with the radioiodinated beta-subunit of oLH, 0.5 +/- 0.1 h for radioiodinated oLH, and 0.7 +/- 0.2 h for the alpha-subunit of oLH recombined with the radioiodinated beta-subunit of oLH. In general, the levels of radioactivity that were intracellular and the rate of degradation of the hormone were inversely related to the quantities of hormone that remained on the plasma membrane. The preparations that contained the beta-subunit of hCG were all internalized at a slower rate (t1/2 = 9-22 h) and consequently were degraded more slowly than any of the preparations that contained the beta-subunit of oLH (t1/2 = 0.5-0.7 h). When the radioiodine in oLH was present in the beta-subunit, intracellular levels of radioactivity were higher and degradation occurred more rapidly than when the radioiodine was in the alpha-subunit. Although the differences were less dramatic, hCG with radioiodine in the beta-subunit also reached higher levels intracellularly, but was degraded to a lesser extent at 16 and 24 h than was hCG with radioiodine in the alpha-subunit. These data demonstrated a dramatic difference (approximately 30-fold) in the rate of loss of oLH vs. that of hCG from the membrane of ovine luteal cells. Further, it appears that the beta-subunit of each of the two hormones is the major factor in determining the rate of internalization of the intact hormone. The differences is how the two hormones are processed at the receptor level may help explain the known differences in their steroidogenic potencies.

Animals↗
PubMed1982

A study of the first eight hours in the stabilization of plasma testosterone concentration in the hemicastrated rat.

Plasma levels of testosterone fell within 4 h after hemicastration in the mature male rat, and recovered within 8 h, without a compensatory rise in plasma LH from 5 to 480 min after surgery. Pulsatile release of LH was not observed in any group, suggesting the possibility that its alteration was not stimulating the single testis. Luteinizing hormone releasing hormone (LH-RH) stimulated plasma LH concentration equally in both control and hemicastrated rats, rising more sharply only in sham-hemicastrated rats treated with a low dose of LH-RH. Plasma LH rose significantly at the same time (6h after surgery) in both castrated (in one step) and hemicastrated rats which were castrated (in two steps). Bilateral denervation of the testis did not affect the response of plasma testosterone after hemicastration. There was a remarkably similar response in both plasma LH and testosterone levels to handling, blood collection, anaesthesia, sham-surgery and hemicastration separately or in combination. It was concluded that the response of testosterone to hemicastration was neither related to early changes in plasma LH levels nor to alterations in the hypothalamo-hypophysial axis.

Animals↗
PubMed1982

Response of testosterone to hemicastration in the testicular vein of the mature rat.

A rapid procedure was developed and validated for collection of testicular vein blood from rats. Samples were collected from both testes and the heart within 2-5 min of transfer of the rat to the anaesthesia jar. There was no difference in levels of testosterone in testicular vein serum between successive samples from the same testis or alternate samples from paired testes. Both hemicastration and sham-hemicastration significantly depressed levels of testosterone in testicular vein serum 4 h after surgery. Peripheral serum testosterone levels were significantly depressed after hemicastration but not sham-hemicastration at 4 h after surgery. By 24 h after surgery, testosterone in testicular vein serum was doubled in the hemicastrated rat, and was restored in the sham-hemicastrated rat, thus achieving normal peripheral testosterone levels in both groups. Similar results were observed in bilaterally denervated rats. These rapid changes could not be attributed to serum LH, which maintained steady levels during the course of these experiments. It was concluded that there are two components in the response to hemicastration: a non-specific response within 4 h to sham-surgery or any other disturbance to the animal, which depresses testosterone output sharply, and a specific response within 24 h to hemicastration, which doubles testicular output. It is the non-specific response after sham-surgery which has simulated and obfuscated the response to hemicastration in the male rat.

Animals↗
PubMed1978

Blood-collecting methodology does not affect the maturational pattern of serum hormone concentrations (testosterone, LH, FSH and prolactin) in the male rat.

Serum hormone levels of blood collected within 1 min by cardiac puncture following ether anesthesia were compared to those of blood collected by decapitation in male rats 30, 60, and 90 days of age. Neither testosterone (T) nor LH was affected by the method of blood collection. Serum FSH was significantly elevated in blood collected by cardiac puncture, and 30-day old rats were the most sensitive to this effect. Serum prolactin (Prl) was significantly elevated in all age groups when blood was collected by cardiac puncture. Both blood-collecting methods demonstrated that, in the 3 ages tested, serum T increased with age, LH and FSH decreased with age, and Prl did not change with age, indicating that blood collection by cardiac puncture is as valid a method as is decapitation for assessing serum hormone levels during maturation.

Aging↗
PubMed1978

Daily rhythmicity of serum testosterone concentration in the male laboratory rat.

Daily rhythmicity of serum testosterone concentration in the mature male laboratory rat was examined under various lighting schedules. In rats living in a standard light cycle (12-h light, 12-h dark; lights on at 0600 h), a trimodal rhythm was predominant, with elevations near 0200, 1200, and 1800 h. This pattern was reasonably stable in seven different studies, despite differences in experimental design, method of blood collection, anesthesia, and whether individual rats were sampled once or repeatedly, and was found both in groups of animals and in individuals, including a study using 40-day-old rats. In constant illumination, the pattern was disrupted, but in constant darkness the trimodal pattern was maintained, indicating that the rhythm is endogenous. In a reversed light cycle (12-h dark, 12-h light; lights on at 1800 h), the "midday" elevation was reversed; in an altered light cycle (12-h dark, 12-h light; lights on at 2300 h), the time of the "midday" elevation was shifted. Serum testosterone concentration was higher during the light phase than the dark phase, and was higher in constant light than in constant darkness. A seasonal shift in the daily rhythmicity of serum testosterone concentration is suggested. The trimodal rhythmicity contrasts with the circadian rhythmicity of other hormones. Its functional role in the life of the animal is unknown.

Animals↗
PubMed1975

Characterization and physiological validation of a radioimmunoassay for plasma testosterone in the male rat.

A radioimmunoassay (RIA) to measure testosterone concentration in the plasma of male rats was formalized, tested and physiologically validated. The procedure measured testosterone equally well, whether or not estimation of recovery and chromatographic purification preceded the RIA. The results were equivalent to those achieved by the method of competitive protein binding. No 17beta-hydroxy-5alpha-androstan-3-one was found in the plasma of male rats. Adrenalectomy did not significantly decrease plasma testosterone in either male or female rats. The simplified protocol met all requirements of precision, sensitivity, accuracy and specificity. A single investigator can analyze 1,000 plasma samples for testosterone in one week if necessary.

Animals↗