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In four studies secretion patterns of LH, FSH, prolactin, testosterone and progesterone were measured in male and female cattle to determine endocrine changes associated with sexual maturation. Two periods of increasing gonadotrophin secretion were observed, the second one coinciding with puberty. A short luteal phase of 8-12 days precedes the first oestrus at 10-11 or 14 months of age. The testosterone values of the bulls increased with age from 5-6 months. Prolactin levels in the bulls increased at the time of the first testosterone rise. A frequency of about 1-2 LH and FSH pulses/8 h occurred at 1, 2, 5 and 10 months of age. The pituitary response to GnRH (1 tig/kg i.v.) was tested in 2 male and 2 female calves at monthly intervals. LH and FSH were released at all ages but a reduced FSH response occurred in both sexes after the 5th month. A small testosterone release was observed as early as 1 month after birth in males similar to those observed after endogenous LH pulses. We conclude that the initiation of puberty in both sexes is controlled by the same neuroendocrine mechanisms. The pituitary gland, ovaries and testes are already able to respond to specific stimuli long before puberty, and they may also be involved indirectly due to changes in the feedback system modulating gonadotrophin secretion.

The lysosomal stabilizer and anti-malarial agent, chloroquine, stimulated the respiration and motility of fresh and aged bovine spermatozoa stored in vitro. Duplication of these effects by the phosphodiesterase inhibitors, theophylline and caffeine, suggested that enhancement of sperm activity by chloroquine may be mediated by cyclic AMP.

Summary. In 2 prepubertal bulls 10-min blood samples collected during a 24-h period showed that gonadotrophin and testosterone peaks occurred regularly at intervals of 6 h in one animal and 8 h in the other. There was a clear relationship between the LH, FSH and testosterone peaks. The increase of gonadotrophin levels was followed 20 \ m=+-\ 6 (s.d.) min later by an increase of testosterone; the interval between the peak values was 61\m=+-\9(s.d.) min. The pattern of prolactin concentrations differed; there were two prolonged elevations rather than regular peaks.