No abstract

A simple approach was developed for determining the number of replicates needed per treatment group to provide experiments of known power and sensitivity, where power equals the probability that a treatment effect would not go undetected if an effect existed and sensitivity equals the minimal treatment response that will be detectable. This approach, in turn, was used to construct reference tables, applicable across scientific disciplines, from which researchers may read replication requirements directly with ease, speed and reliability. To use the tables, one need only furnish a reliable estimate of the coefficient of variability expected among replicates, which may be obtained from prior observations on similar populations. The tabular data also enable a rapid, reliable assessment of the actual power and sensitivity of completed experiments, such as those contained within the published literature.

Plasma and tissue testosterone concentrations were determined by radioimmunoassay in 12 eight-month-old sexually mature New Zealand White rabbits and evaluated for possible associations with spermatogenic efficiency as well as with volume density and number of Leydig cells. Testicular tissue was processed histologically and histometry was performed in order to quantify germ cells, Sertoli cells and Leydig cells. Spermatogenic efficiency, reported as the ratios among germ cells (spermatogonia, primary spermatocytes and round spermatids) and by the ratio of germ cells to Sertoli cells, was not associated with testosterone levels. However, Leydig cell parameters such as number of Leydig cells per gram of testis, total number of Leydig cells per testis and percent cell volume of Leydig cell nuclei were correlated significantly with testosterone levels. The statistically significant correlation (r = 0.82, P<0.05) observed between testosterone levels and the number of Leydig cells per gram of testis suggests that, in the rabbit, the latter parameter can serve as a criterion for monitoring testosterone levels in this species under normal conditions. Correspondence

Extended semen from six Hereford bulls was placed in .25-ml Continental straws and frozen in the vertical position. Treatments were arranged factorially with glycerol levels of 5, 7, 9 or 11%; semen cooled from 5 to-130 C in 3.5 (fast), 20 (moderate) or 40 min (slow); and thawed in water at 5 C for 3 min, 35 C for 12 sec, 55 C for 8 sec, 75 C for 7 sec or 90 C for 5 seconds. Fast freezing resulted in greater postthaw motility than moderate (P < .05) or slow rates (P < .01), regardless of thawing method. Glycerol levels of 7 to 11% provided optimal survival when averaged over rates of freezing and thawing (P < .05). Post-thaw motility improved as the temperature of the thawing bath was increased from 5 to 55 C (P < .01). Further increases in thawing bath temperature to 90 C did not enhance survival. The post-thaw motility of spermatozoa frozen rapidly in straws and thawed at 55 to 90 C exceeded that for ampules from split-ejaculates frozen in 1.0-ml ampules (P < .01). Semen from one Angus, two Hereford and three Charolais bulls was frozen in a second study at the fast, moderate and slow rates in straws maintained in the horizontal or vertical position. The final extended semen contained 5, 7, 9 or 11% glycerol; and all semen was thawed in 75 C water for 7 seconds. Fast freezing resulted in post-thaw motility equal to

SUMMARY Polydimethylsiloxane (PDS) capsules providing surface areas of 50, 75, 100, 200, 400 and 2000 mm2 were filled with testosterone, testosterone cypionate (TC), or testosterone propionate (TP) and were implanted (s.c.) into sexually mature rats for 56 days to determine the efficacy of this mode of androgen administration in suppressing or maintaining spermatogenesis. Rats that received 75 mm2 capsules of TP and 200 mm2 capsules of testosterone or TC were azoospermic and had a 45–50% reduction in testicular weight. Moreover, immunoreactive serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations declined eightfold below control values, but plasma testosterone titres and the dry weight of the accessory sex glands were not affected (P > 0·10). Conversely, 2000 mm2 capsules of testosterone, TC or TP maintained testicular weight and induced accessory sex gland hypertrophy as well as a five- to eightfold increase in the concentration of plasma testosterone. The relative number of germ cells at stage VII of the cycle of the seminiferous epithelium was not affected (P > 0·15) by 2000 mm2 testosterone capsules even though immunoreactive serum LH and FSH concentrations remained at least eight-fold below control values. Similar implants containing TC or TP maintained germ cell numbers within 83% of control testes. The results establish that PDS capsules releasing 'low' doses of testosterone, TC or TP induce azoospermia without affecting plasma testosterone concentration or accessory sex gland weight, and that similar capsules releasing 'high' doses of testosterone maintained spermatogenesis quantitatively up to and including step 7 of spermiogenesis.

Testes were obtained from 34 Hereford or Angus bulls at about 1.5 yr of age and were used to investigate the relationship between the absolute number of Sertoli cells vs testicular size and daily spermatozoal production (DSP). Quantitative determination of DSP was based upon enumeration of elongated spermatids in testicular homogenates. The ratio of step 8 spermatids to Sertoli cells (S:SC) was established by direct counts of these cells in each of 20 round stage VIII seminiferous tubular cross sections for each bull. The number of Sertoli cells per paired testes was calculated as (total spermatids divided by S:SC)/.394, where total spermatids equalled the number of homogenization-resistant spermatids. The factor of .394 adjusted for the fact that the latter cells are present for only 39.4% of the spermatogenic cycle. All data were subjected to simple linear and second-order regression analyses. A positive linear relationship (P less than .005) was found between testicular weight (Y, in grams) and the absolute number of Sertoli cells per paired testes (X, in billions), which was characterized by the equation Y = 315.2 + 10.74X and a coefficient of correlation (r) of .56 (P less than .01). A similar relationship was observed between DSP (Y, in billions) and Sertoli cell numbers (X, in billions). This was characterized by the equation Y = 1.36 + .222X (P less than .005) and a coefficient of correlation of .70 (P less than .01). Daily sperm production was unrelated to the S:SC ratio (P greater than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Testes from 37 Holstein bulls, 38-99 mo of age, were used to investigate the relationship of Sertoli cell number, Sertoli cell-germ cell ratios and other related factors to daily sperm production (DSP). DSP was assessed by enumeration of spermatids in testicular homogenates, whereas Sertoli cell and germ cell ratios were based on direct counts in 20 round Stage VIII seminiferous tubular cross sections per bull. Numbers of Sertoli cells were calculated as (total homogenization resistant spermatids:spermatid:Sertoli cell ratio)/0.394; the factor of 0.394 adjusted for the presence of homogenization resistant spermatids during only 39.4% of the spermatogenic cycle. Data were subjected to simple linear and second-order regression analyses. Positive linear relationships were observed between DSP and testicular parenchymal weight (p less than 0.005, R = +0.71), DSP per gram (p less than 0.005, R = +0.79), total Sertoli cells (p less than 0.005, R = +0.83), Sertoli cells per gram (p less than 0.01, R = +0.47) and the yield of Step 8 spermatids per Type A spermatogonium (p less than 0.05, R = +0.34). DSP was not related (p greater than 0.10) to the number of germ cells supported per Sertoli cell. Testicular parenchymal weight and DSP per gram were unrelated to each other (p greater than 0.10), but both were related (p less than 0.005) to the total Sertoli cell number (R = +0.61 and +0.62, respectively). Total number of Sertoli cells accounted for more of the variation in DSP between bulls (R2 = 68.2%) than did any other factor examined. It was suggested that total Sertoli cell number may be an important determinant of a bull's spermatogenic potential.

Testes from 47 stallions, 1-20 yr of age, were used to examine the influence of age on Sertoli and germ cell populations as well as on functional activity of Sertoli cells. For these stallions, the number of Sertoli cells per paired testes declined linearly with age, and was only 41.7% as great at age 20 as at age 2. However, development of reproductive organs proceeded until age 12-13, as evident from increases in paired testes weight and quantitative rates of spermatozoal production. Although the absolute number of Sertoli cells declined during this period of development, individual Sertoli cells displayed a remarkable capacity to accommodate greater numbers of developing germ cells. Between age 2 and age 12, the mean numbers of developing spermatogonia, young primary spermatocytes, old primary spermatocytes, and round spermatids supported by each Sertoli cell at Stage I of spermatogenesis increased by 49, 176, 153, and 161%, respectively.