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Summary. Response of the cryptorchid testis to gonadotrophic stimulation was assessed by comparison of the androgen production capability in vivo and in vitro with that of the normal scrotal testis. Serum androgen concentrations in cryptorchid rats were similar to those in normal rats, and the incremental increase 60 min after 50 i.u. hCG (i.v.) was about 7-fold for both groups. Basal and hCG-stimulated androgen production in vitro was higher for abdominal testes (557 and 3286 ng/pair) than for scrotal tests (157 and 504 ng/pair). Specific binding of hCG by testicular homogenates was slightly higher (P < 0·05) for cryptorchid testes when expressed per unit weight, but Scatchard analysis indicated that although hCG binding affinities did not differ (K _a = 2 × 10¹⁰ m ⁻¹), hCG binding capacity of cryptorchid testes was only 75 ng, compared to 219 ng for scrotal testes. These data indicate that a discrepancy exists between androgen production in vivo and in vitro by cryptorchid testes and that normal serum androgen concentrations are maintained in the presence of decreased numbers of testicular LH/hCG receptors.

Summary. Surgically induced cryptorchidism in rams resulted in elevated serum concentrations of LH but near-normal concentrations of androgen (testosterone and 5α-DHT). Injections of ovine LH (2 × 50 μg; 2 × 500 μg) resulted in maximal androgen secretion in the intact rams and similar but lower concentrations in cryptorchid rams. Peak concentrations were 14·9 and 8·5 ng/ml in the intact and cryptorchid rams respectively (P < 0·05).

Summary. Heifers were treated with saline (Group I, N = 10), keyhole limpet haemocyanin (KLH; Group II, N = 10), androstenedione-KLH antigen (Group III, N = 14), or oestradiol-17β-KLH antigen (Group IV, N = 14). Booster injections were given to produce binding of > 10% at dilutions of 1:100 to 1:1000 (50% binding = 14·4 pg androstenedione and 9·5 pg oestradiol). The heifers were mated and killed at ∼46 days of gestation to establish ovulation rates, calf numbers, blood hormone relationships and ovarian morphology.

Ovulation rate in animals immunized against androstenedione (Group III) was significantly greater than in the other groups; 4 of the animals had double ovulations and 3 had twins. No significant differences were found between Groups I, II and IV in relation to ovulation or pregnancy rate and animals immunized against oestradiol-17β continued to cycle and become pregnant. Systemic progesterone, androstenedione and oestrogen levels were generally increased in Groups III and IV but the differences were not significant. No differences were detected between treatment groups in relation to CL weights, ovarian weights, follicle sizes or numbers. No binding of [₃H]androstenedione or [³H]oestradiol-17β was detected in allantoic or amniotic fluids or fetal serum. Maternal antibody binding was correlated with binding of [³H]androstenedione and [³H]oestradiol in the follicular fluid sampled from the two largest follicles in the ovaries of each animal (Group III, r = 0·59; Group IV, r = 0·60; P < 0·05). The response of increased ovulation rate in cattle immunized against androstenedione should be further investigated to study follicular recruitment and increased productivity.

Summary. Sexually mature rams were left intact, castrated (wethers), castrated and implanted with testosterone, or castrated, implanted with testosterone and pulse-infused every hour with LHRH. Serum concentrations of LH increased rapidly during the first week after castration and at 14 days had reached values of 13·1 ± 2·2 ng/ml (mean ± s.e.m.) and were characterized by a rhythmic, pulsatile pattern of secretion (1·6 ± 0·1 pulses/h). Testosterone prevented the post-castration rise in serum LH in wethers (1·0 ± 0·5 ng/ml; 0 pulses/h), but a castrate-type secretory pattern of LH was obtained when LHRH and testosterone were administered concurrently (10·7 ± 0·8 ng/ml; 1·0 pulse/h). We conclude that the hypothalamus (rather than the pituitary) is a principal site for the negative feedback of androgen in rams and that an increased frequency of LHRH discharge into the hypothalamo—hypophysial portal system contributes significantly to the post-castration rise in serum LH.

Summary. Twelve non-implanted crossbred bull calves served as controls and 30 crossbred bull calves (10/treatment) were implanted for 82 days, beginning at 34 days of age, to determine the influence of testosterone propionate (TP), dihydrotestosterone propionate (DHTP) and oestradiol-17β (E2) on prepubertal and pubertal pituitary–testicular function and on postpubertal social and sexual behaviour. Compared with control bulls, concentrations of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and inhibin concentrations were suppressed (P < 0·01) in all implanted bulls. Testosterone (T) concentration increased (P < 0·001) in TP-implanted, but decreased (P < 0·01) in DHTP and E2 bulls during the implant period. LH response to gonadotrophin-releasing hormone (GnRH) challenge during the implant period (2·5 months of age) was less (P < 0·01) in TP, E2 and DHTP bulls than in controls. A small but significant T response to GnRH occurred in control bulls at 2·5 months of age. LH and T responses to GnRH challenge at 7 months of age (100 days after implant removal) was similar (P > 0·20) in control and implanted bulls. Steroid implants administered prepubertally had no effect (P > 0·10) on postpubertal social and sexual behaviours, including number of flehmen responses, abortive mounts, services and competitive order score. Body weight did not differ (P > 0·10) between treatment groups, but testis size was reduced (P < 0·01) during the implant period and up to 10 months of age in treated bulls compared with controls. Testes remained smaller in E2-treated bulls up to the end of the study (23 months of age), but daily sperm production and epididymal weight did not differ (P > 0·10) between treatment groups at slaughter. Control bulls reached puberty earlier (P < 0·01; 270 ± 11 days of age) than did TP (302 ± 11 days), DHTP (309 ± 11 days) or E2 (327 ± 11 days) bulls. Although puberty was delayed in all implant groups, there was no difference in scrotal circumference at puberty (average 28·4 ± 0·4 cm) between treatment groups. Our findings indicate that TP, DHTP and E2 implants administered prepubertally result in acute suppression of serum LH, FSH and inhibin during the implant period and in post-implant suppression of testis size and delayed puberty in bulls. The lack of treatment effect on behaviour suggests that steroidal programming of sexual behaviour occurs before 1 month of age in bulls.

Keywords: implants; steroids; gonadotrophins; behaviour; bull

The role of LHRH in modulating intrapituitary LH content as well as the distribution of LH among its isoforms was examined in sheep. Rams (n = 3) and wethers (n = 6) were actively immunized against an LHRH–human serum globulin conjugate. Pituitaries collected from these animals plus pituitaries from corresponding numbers of nonimmunized rams and wethers were extracted with a buffered saline solution containing protease inhibitors. Immunization markedly reduced total amounts of immunoreactive LH in the pituitary. An aliquot of each pituitary extract was desalted by flow dialysis against water and chromatofocused on a pH 10.5–7.0 gradient. Concentrations of LH in chromatofocusing fractions were determined by radioimmunoassay. LH in pituitary extracts resolved into nine peaks during chromatofocusing which were coded with letters beginning with the most basic isoform. The percentage of LH as the two most basic isoforms, A' and B, was similar (P > 0.05) in all treatment groups. Isoform H constituted a higher percentage (P < 0.05) of the LH in both castrate groups. Nonimmunized wethers had higher percentages of isoforms C, D and E (P < 0.05) and lower percentages (P < 0.05) of the acidic isoforms (coded as peak Z herein) than did other treatment groups. Thus, castration shifted the pattern of intrapituitary isohormones towards the more basic forms. Nonimmunized rams had a higher percentage (P < 0.05) of isoform G than did other groups. Isoform F, the most abundant isoform, was present as a higher percentage (P < 0.05) in immunized rams and wethers than in nonimmunized animals. Hence, ablation of hypothalamic LHRH reaching the pituitary by active immunization not only markedly reduced the quantity of LH in the pituitary, but also altered the distribution of LH among its isoforms yielding a higher percentage of the most abundant isoform F. Hypothalamic LHRH therefore not only increases the quantity of LH in the pituitary but also alters the pattern of intrapituitary isohormones by reducing the percentage present as isoform F. Furthermore, inputs from both the hypothalamus and gonads appear to regulate the distribution of intrapituitary isohormones with hypothalamic influences predominating.

Summary. Testosterone-filled Silastic capsules were implanted into mature rams at the time of castration (wethers). After 6 weeks, a tonic pattern of FSH secretion was observed in rams, wethers and wethers implanted with testosterone. Castration caused serum concentrations of FSH to increase 4–5-fold. Relatively low serum concentrations of testosterone (25–50% of intact ram values) did not significantly affect FSH secretion in wethers, but wethers exposed to concentrations of testosterone equivalent to those of intact rams had serum concentrations of FSH similar to those of intact rams. We suggest that testosterone feedback can account for the gross differences in FSH observed between intact and castrated male sheep.

Summary. Mature Suffolk ewes were either actively or passively immunized against the synthetic fragment of porcine inhibin alpha, pIα(1-30), to determine the effects on gonadotrophin secretion and ovulation rate. Thirteen control ewes were immunized against human serum albumin, 12 ewes were actively immunized against pIα(1-30) and 36 ewes were passively immunized with pIα(1-30) antiserum. Blood samples were collected at 4-h intervals for 72 h from oestrus-synchronized ewes following the withdrawal of the progestagen pessaries. Mean gonadotrophin concentrations measured during the oestrous cycle of control ewes, ewes actively immunized against pIα(1-30) and ewes passively immunized against pIα(1-30) were similar, but their secretory profiles differed. Serum concentrations of follicle-stimulating hormone (FSH) were highest in ewes which had received antiserum at the time of pessary withdrawal; FSH concentrations did not decrease during the follicular phase of the oestrous cycle in ewes given antiserum 24 h after pessary withdrawal. Subtle but significant increments in serum FSH concentrations were observed in all passively immunized ewes in which sampling commenced at the time of treatment. The amplitude of the preovulatory luteinizing hormone (LH) peak, but not of the FSH peak, and the postovulatory secondary rise in FSH were lower (P < 0·05) in actively immunized ewes than in control ewes. The mean (±s.e.) ovulation rate for actively immunized ewes (6·6 ± 1·0) was 3 times higher (P < 0·05) than that for control ewes (2·0 ± 0·2), but was unaffected by passive immunization (range, 1·8–2·3). The divergent results involving serum gonadotrophins and ovulation rate following active or passive immunization to the same pIα(1-30) immunogen suggest that changes in circulating gonadotrophins alone may not account for the increased ovulation rate in immunized Suffolk ewes.

Keywords: inhibin; fecundity; LH; FSH; immunization; sheep

Summary.

Carnitine acetyltransferase activities have been determined in the testes of developing and cryptorchid rats. This enzyme appears to be associated with the primary spermatocytes and early spermatids of the rat testis since activities increased markedly when these cells were proliferating. The usefulness of carnitine acetyltransferase as a `marker enzyme' in the spermatogenic process is re-emphasized. Serum testosterone levels in the same animals closely paralleled the increased enzymatic activity (r = 0·59; P<0·01). The testes of rats made experimentally cryptorchid contained reduced activity of carnitine acetyltransferase. The enzyme activity of 1-day cryptorchid testes was reduced to approximately half, and the activity of 10-day cryptorchid testes was reduced to one-sixth that of normal adult testes.

A number of experiments have shown that the mammalian testis is quite sensitive to changes in atmospheric gases, both in vivo and in vitro. Degenerative changes have been observed in testes of rodents exposed to abnormal levels of oxygen, neon, carbon monoxide and other elements (Cockett & Johnson, 1970).

High levels of carbon dioxide appear deleterious to general systemic responses (Mullenax & Dougherty, 1963) and to sperm cell integrity and male fertility (Mukherjee & Singh, 1967) in vivo; alterations in atmospheric CO₂ levels affect metabolism of sperm cells (Salisbury, VanDemark, Lodge & Cragle, 1960) and testicular tissue (Fleeger, VanDemark & Johnson, 1967) in vitro. The changes in testes in vivo following short-term exposure of animals to elevated CO₂, however, have not been reported. This study