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T. A. Parkening, T. J. Collins and E. R. Smith

Plasma levels of LH were measured in young sexually mature (2- to 5-month-old) and aged (13- to 20-month-old) female C57BL/6 mice, Syrian hamsters and Wistar rats using a radioimmunoassay (RIA) and a radioreceptor assay (RRA). There were no statistically significant differences when comparing data from the two assays when examining young oestrous and dioestrous mice. Aged oestrous and dioestrous mice exhibited significantly higher levels of LH as measured by RIA than by RRA. Levels of LH analysed by RIA were also higher in aged mice compared with those in younger mice. Comparing LH concentrations with the two types of assays in younger dioestrous and aged anoestrous hamsters produced similar results. In contrast, aged pseudopregnant rats exhibited significantly lower levels of plasma LH than younger dioestrous females and there were no differences in RIA and RRA values. There were also no differences when comparing data from the two assays in younger rats. The mean (± s.e.m.) RRA: RIA ratios of 0·96 ± 0·05 (oestrous) and 0·96 ± 0·04 (dioestrous) for younger mice and 0·92 ± 0·08 for younger hamsters were significantly higher than the ratios of 0·66 ± 0·72± 0·05 and 0·71 ± 0·05 respectively of their aged counterparts. The mean RRA: RIA ratios in the two age groups of rats were almost identical (0·79 ± 0·05 and 0·80 ± 0·10). These studies suggested that a portion of the higher LH levels detectable by RIA in some aged female rodents results from qualitative changes in the LH molecule.

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T. A. PARKENING, S. K. SAKSENA and I. F. LAU

* Department of Anatomy, University of Texas Medical Branch, Galveston, Texas 77550, U.S.A. and †The Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545, U.S.A.

(Received 5 December 1977)

Fertilization is delayed approximately 2–5 h in the majority of ova recovered from aged hamsters (14–17 months old), compared with younger (3–5 months old) animals (Parkening & Soderwall, 1975). This delay may explain the relatively large percentage (40%) of ova which is incapable of developing to the implantation stage in this species (Parkening & Soderwall, 1975). Blaha & Leavitt (1974) have shown that there is a wider variation in the peripheral plasma concentration of progesterone at the time of fertilization in aged than in younger hamsters. A hormonal imbalance in the senescent female hamster may disturb normal gamete interactions, thus causing the delay in fertilization. In order to determine the significance of hormonal levels with respect to fertilization, the concentrations of progestogens,

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A. Bartke, W. W. Morgan, R. N. Clayton, T. K. Banerji, A. M. Brodie, T. A. Parkening and T. J. Collins

ABSTRACT

In several species, including man and the rat, hyperprolactinaemia is associated with suppression of gonadotrophin release and male sexual behaviour. However, in the hyperprolactinaemic male mouse, plasma LH and FSH levels and copulatory behaviour are increased rather than suppressed. In an attempt to identify mechanism(s) which may be responsible for these effects of hyperprolactinaemia in the mouse, we have examined the effects of two ectopic pituitary isografts on several indices of hypothalamic and pituitary function in adult DBA/2J males. Animals with pituitary grafts had markedly increased plasma concentrations of prolactin, LH and FSH and enlarged seminal vesicles, whereas testicular and pituitary weights were not affected. Content of LHRH receptors and activity of aromatase in the pituitary, as well as dopamine-β-hydroxylase activity in the hypothalamus were nearly identical in pituitary-grafted and sham-operated males. Biosynthesis of dopamine and turnover of noradrenaline in the median eminence were significantly increased in grafted males. We suggest that the increase in the activity of hypothalamic noradrenergic neurones may mediate stimulatory action of hyperprolactinaemia on LH and FSH release in the mouse. Comparison of these results with those obtained previously in the rat suggests that species differences in the effects of prolactin on gonadotrophin release may be related to its divergent effects on noradrenaline turnover.

J. Endocr. (1987) 112, 215–220