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L. L. EWING and N. L. VANDEMARK

Summary.

Investigations were conducted on the in-vitro metabolic activity of rabbit testicular tissue after exposing the testis to abdominal temperatures for 2, 6 or 24 hr. Metabolic activity increased with the shorter exposure and then significantly decreased as compared with that of normal testicular tissue. Tissue treated in this way recovered its normal metabolic activity when subjected for 30 min to an ice-cold glucose solution. Tissues exposed to abdominal temperature for 24 hr were found to contain 12% less glucose and 27% less lactic acid than control tissues. This study suggests that spermatogenic arrest which results from exposure of the testis to elevated temperatures may be caused by reduced levels of substrate in the tissue.

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L. L. EWING and N. L. VANDEMARK

Summary.

In several investigations of the effect of higher than normal scrotal temperatures on metabolic activity of rabbit testis, oxygen uptake, glucose utilization and lactic acid accumulation of testicular tissues were compared with those of kidney cortex slices. Also, glucose utilization and rate of blood flow through the isolated, perfused rabbit testis were measured. When an adequate amount of substrate (0·055 m glucose) was present, the enzyme systems of neither testis nor kidney cortex slices were deleteriously affected by increased temperature (36·5° C versus 39·0° C) in vitro. An increased temperature in vitro caused a decreased glucose uptake by the isolated, perfused rabbit testis. This decrease in glucose uptake corresponded with a decrease in the amount of glucose available to the tissue, as a result of decreased blood flow and increased metabolic activity. These observations further suggest that spermatogenic arrest due to elevating testicular temperature may be caused by a substrate deficiency to the tissue.

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N. L. VANDEMARK and L. L. EWING

Summary.

A simple and inexpensive apparatus for perfusing the mammalian testis has been developed. Glucose utilization, rate of blood flow, and histological examination have indicated maintenance of certain areas of the isolated organ. Successful perfusions have been carried out over a 7-hr period. Preliminary findings suggest that nutrient requirements of the testis may be determined by this technique.

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G. H. STABENFELDT, L. L. EWING and L. E. McDONALD

Summary.

Progesterone was determined daily in the peripheral plasma of six cows for a total of seven complete oestrous cycles. Progesterone levels ranged from less than 0·5 ng/ml plasma during the follicular phase to 6·6 ng/ml plasma (6·1 to 10·2 ng) at peak luteal phase. Progesterone levels in cows with 21-day cycles increased rapidly from Day 3 to Day 8 (oestrus = 1) with a much slower rate of increase from Day 8 to Day 17. These cows showed a progesterone decrease of more than 50% from the previous day on Days 18 (two cows), 19 (one cow) and 21 (two cows). Two other cows with cycles of 22 and 23 days' duration both had a similar decline on Day 20.

A variable time interval of 1 to 5 days was observed between the decline of progesterone and the occurrence of oestrus. These data indicate that considerable variation may exist among cows as to time requirements for follicle development and maturation.

Monitoring of peripheral levels of progesterone is suggested as a means of studying corpus luteum function.

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L. G. STRATTON, L. L. EWING and C. DESJARDINS

Summary.

Experiments were designed to examine the release of testosterone through polydimethylsiloxane (PDS) capsules in vitro and in situ and to test the efficacy of PDS capsules in maintaining testosterone in the peripheral circulation of castrate male rabbits for several months. The results demonstrate that (1) tritiated testosterone passed through PDS capsules suspended in water, (2) the tritiated material released into water had the same chromatographic mobility as authentic testosterone when subjected to thin-layer chromatography, (3) the rate of release of testosterone into water was dependent upon capsule surface area, (4) the release of testosterone from implants in situ was dependent upon surface area but independent of implantation site (i.e. subcutaneous versus intraperitoneal implants), and (5) the release of testosterone from PDS capsules in situ remained relatively constant over a span of 3 months. Castration abolished libido and caused accessory sex organ atrophy in male rabbits, but subcutaneous placement of testosterone-filled PDS implants (430 mm2, 0·245 mm thick) maintained these androgen-dependent characteristics at normal levels. The concentrations of seminal fructose, citric acid and plasma testosterone noted in castrate rabbits receiving testosterone implants in situ were virtually identical to those noted in intact rabbits receiving similar implants containing cholesterol for 3 months.

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L. L. EWING, L. G. STRATTON and C. DESJARDINS

Summary.

Testosterone-filled polydimethylsiloxane (PDS) capsules (0·245 mm wall thickness) were placed subcutaneously in normal adult male rabbits to assess the relationship between the surface area of the implant and the amount of testosterone released. Testosterone release was quantified in terms of plasma testosterone concentrations and other biological endpoints such as libido, accessory sex organ weight, seminal fructose and citric acid levels and spermatogenic activity. Subcutaneous placement of PDS capsules ranging from 100 to 800 mm2 in surface area had no measurable (P>0·25) effect on (1) plasma testosterone concentrations, (2) libido, (3) accessory sex gland weight, and (4) the concentrations of fructose and citric acid in seminal fluid. The total daily sperm production and the number of step-6 spermatids decreased linearly with each successive increase in capsule surface area. It was concluded that testosterone-filled PDS capsules (800 mm2) induced azoospermia in rabbits without any significant (P>0·25) alteration in either plasma testosterone or the weight and secretory activity of the accessory sex glands.

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R. C. Cochran, A. W. Schuetz and L. L. Ewing

Summary. Conversion of labelled 5α-androstan-17β-ol-3-one (DHT) by isolated testicular cells from rats of different ages was examined under saturating substrate conditions in vitro (5–10 μg DHT/ml in a 24 h incubation). Two detectable metabolites of DHT were produced by testicular cells in vitro, 5α-androstane-3α-17β-diol (3α-diol) and 5α-androstane-3β,17β-diol (3β-diol). Production of these diols during a 24 h period was linear, and the amounts formed were directly related to the cell number. The amount of 3α- and 3β-diols formed by testicular cells of rats of different ages increased from Day 10 to Day 25, then declined. Testicular cells from rats 10 to 20 days of age converted DHT mainly to 3α-diol, but thereafter 3β-diol was the predominant testicular metabolite of DHT.

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B. I. OSBURN, G. H. STABENFELDT and L. L. EWING

Summary.

The inoculation of viable cultures of Vibrio fetus into the uterus of cows in the second and third 3-monthly periods of pregnancy resulted in abortion. All foetuses exposed during the second 3 months were aborted 5 to 7 days post-inoculation; foetal death occurred several days before expulsion. Peripheral plasma progesterone levels declined at the time of foetal death.

Cows injected with V. fetus during the third 3 months of pregnancy aborted 9 to 20 days post-inoculation and in a majority of cases delivered live calves. The decline of progesterone levels on the day of abortion is very similar to that observed before normal parturition. Progesterone levels in the dam reflect the viability status of the foetus. The decline of progesterone associated with abortion may be due both to placental dysfunction as well as luteolysis of the cl because of the release of products from the infected foetus.

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L. L. EWING, GEORGE BRANT and K. E. EBNER

Summary.

The effect of chronic cold stress for periods of 0, 3, 5, 10, 20 and 30 days on metabolic activity in vitro, testis weight, total lipid, total carbohydrate, total carbohydrate on lipid free residue, ribonucleic acid (rna), deoxyribonucleic acid (dna) and percentage of lipid free dry weight of the testis was determined. Metabolic activities measured were endogenous oxygen consumption and oxygen uptake in the presence of exogenous glucose, succinate and a Krebs' cycle reaction system. Carbon dioxide, lactic acid production and glucose uptake were also determined. Cold exposure caused a significantly decreased rate of body weight gain and a highly significant transient hypertrophy of the adrenals. There was no significant change in the metabolic activity and chemical constituents of the testes. These data indicate that cold stress for 30 days has no significant effect on testis size, composition or metabolic activity in mature rats in which the hypothalamo-adenohypophysial-gonadal axis was stimulated by constant light.

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G. H. STABENFELDT, E. L. AKINS, L. L. EWING and M. C. MORRISSETTE

Summary.

Progesterone levels were determined in the peripheral plasma of four gilts on each day of the oestrous cycle. An initial rise was observed at Day 3 or 4 of the cycle (oestrus = Day 1) followed by a very rapid increase up to Day 7 or 8 and a slower rate of increase until Day 14 or 15 of a 20-day cycle. The highest levels of progesterone during the luteal phase were about 35 ng/ml plasma and the average concentration during Days 10 to 15 was approximately 27 ng/ml plasma. The decline in progesterone levels after Day 15 was precipitous, a thirty-fold decrease occurring in most cases within 48 hr. Progesterone levels remained low (about 0·5 ng/ml) for about 7 days during the phase of follicle growth and ovulation.

A rather consistent time interval (7 days) was observed between the decline in progesterone concentration and the onset of overt oestrus. The high levels of circulating progesterone in the gilt may suppress follicle development sufficiently during the luteal phase so that approximately 1 week is required between corpus luteum regression and ovulation.

The concentration of plasma progesterone in nine castrated boars was 0·9 ng/ml suggesting an extra-gonadal source of progesterone, possibly adrenal in origin.