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- Author: C. B. KATONGOLE x
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SUMMARY
A method is described for the measurement of testosterone in peripheral blood plasma by competitive protein binding, using a 1:80 dilution of human late-pregnancy plasma and Sephadex for separating protein-bound from unbound steroid. The reliability criteria were examined in detail for plasma from bulls and rams. Testosterone was measured with a high degree of accuracy, and with a precision of 4·9–7·9% in the concentration range of 4–24 ng/ml. The specificity of the method was checked by comparing it with a gas-chromatographic technique, and the agreement was good. The testosterone concentrations in the peripheral plasma of bulls and rams were found to range between 2 and 24 ng/ml.
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MRC Unit on the Development and Integration of Behaviour, Madingley, Cambridge and Department of Veterinary Clinical Studies, Cambridge, CB3 8AA
(Received 16 October 1974)
Male behaviour during the reproductive cycle of the Barbary dove begins with courtship behaviour and, after a series of behavioural transitions, progresses to incubation. Male courtship appears to be androgen-dependent because it can be restored in castrated birds by systemic or intrahypothalamic administration of testosterone propionate (Hutchison, 1971). However, progesterone is thought to be causally related to the termination of courtship and the onset of incubation behaviour (Lehrman, 1965). The objects of the present study were to determine (a) whether testosterone (T) is present in the peripheral blood plasma of courting male doves, and (b) whether T levels are similar to those of incubating males when progesterone is thought to be functionally active. Because there is evidence in the male for a transition early in the
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Department of Animal Physiology, University of Nairobi, Chiromo, Nairobi, Kenya
(Received 1 February 1977)
The concentration of testosterone in the plasma of most male domestic and laboratory animals, for example bulls (Thibier, 1975), boars (Andresen, 1976) and rats (Mock, Kamel, Wright & Frankel, 1975) is usually in excess of 10 nmol/l. In seasonal breeders such as sheep, values as high as 90 nmol/l have been reported in the summer before the breeding season (Falvo, Buhl, Reimers, Foxcroft, Dunn & Dziuk, 1975). In contrast, Katongole (1971) found that in a temperate summer, plasma testosterone concentrations in Equidae, including the donkey, were 4·5 nmol/l or less. It was, therefore, of interest to investigate whether the basal plasma testosterone concentrations in donkeys would be higher and more stable in the tropics.
Six potent adult male donkeys were kept in a large pen, fed rhode grass and given free access to salt and water. Blood
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SUMMARY
Three adult Suffolk rams were bled at weekly intervals for 14 months, and at hourly intervals for 24 h during the summer (one ram) and autumn (two rams). Luteinizing hormone (LH) was measured by radioimmunoassay, and testosterone by a competitive protein binding assay.
There were episodic bursts of LH secretion during the 24 h period in both the summer and the autumn; the frequency of discharge was lower in the summer, but the amplitude (0·1–8·0 ng/ml) did not appear to change. It was not always possible to detect seasonal changes in LH concentration in single blood samples taken once a week throughout the year.
The blood testosterone levels also showed marked fluctuations throughout the 24 h, and the frequency of the peaks was lower in the summer. But in contrast to LH, the magnitude of the testosterone peaks also changed throughout the year; from January to September the testosterone concentration ranged from 0·5 to 10 ng/ml plasma, whereas from October to December it ranged from 3 to 28 ng/ml. Thus in temperate regions the ram, like the ewe, shows seasonal changes in gonadal endocrine activity, although some degree of spermatogenesis continues throughout the whole year.
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SUMMARY
Luteinizing hormone (LH) and testosterone were measured in the peripheral plasma of two bulls by radioimmunoassay and competitive protein binding techniques. Samples were collected from an indwelling jugular catheter once an hour for 24 h, and then at more frequent intervals after a number of experimental procedures.
Each bull showed its own characteristic pattern of cyclic LH changes, with 5–10 peaks during 24 h that were apparently unrelated to daylight, feeding or sleep. Each LH peak was associated with a testosterone peak; the LH concentrations ranged from 5 to 50 ng/ml, and those of testosterone from 2 to 20 ng/ml.
Sexual stimulation, such as the sight of a cow, or 'teasing', or on one occasion the act of ejaculation itself, caused an immediate release of a large amount of LH. If the testosterone levels were low at the time, the LH peak was followed by a testosterone peak. But when the testosterone levels were high at the time of LH discharge, the testis seemed to be unable to respond any further. An intravenous injection of 500 i.u. human chorionic gonadotrophin was associated with LH release and caused the testosterone levels to rise to maximal values of 22 ng/ml within 1½ h.
It is concluded that the cyclical pattern of LH release is due to some inherent central rhythm, and that each transient LH peak results in transient maximal stimulation of testicular testosterone secretion.
