Serum and CSF Concentrations of Testosterone and LH Related to Negative Feedback in Male Rhesus Monkeys

This study investigated the relationship of two overt circadian rhythms, locomotor activity and melatonin synthesis in the pineal gland, by comparing their responses to asymmetrical reductions in photoperiod. Transfer of male Syrian hamsters from long to short daylengths led to an increase in the duration of both locomotor activity and the period of melatonin synthesis. Over the course of re-entrainment, the two rhythms were held in a stable phase relationship, and the direction of the switch did not influence the rate of decompression or the final phase relationships established after 8 weeks in short daylengths. Decompression of the activity rhythm was not influenced by pinealectomy. Exposure to short photoperiods caused gonadal regression and a consequent decline in serum testosterone levels from 10 to less than 1 nmol/l. The direction of the photoperiodic switch did not affect the time-course of gonadal regression. These data demonstrate the important influence of photoperiod upon the duration of the nocturnal peak of melatonin production by the pineal and also demonstrate that this effect is one example of a more widespread response of the circadian system. A qualitatively similar signal controls both locomotor activity and melatonin synthesis, although the neural basis of this common mechanism is unclear.

“…Serum testosterone was determined by the method of Dubey, Herbert, Abbott & Martensz (1984). This assay has been used previously for hamster testos¬ terone .…”

Section: Radioimmunoassaymentioning

confidence: 99%

Effect of asymmetrical reductions of photoperiod on pineal melatonin, locomotor activity and gonadal condition of male Syrian hamsters

Hastings

Walker²,

Herbert³

1987

“…The limit of sensitivity was 017 ng/1; inter-and intra-assay coefficients of varia¬ tion were 16-3 and 9-4% respectively. Serum testosterone concentrations were measured by radioimmunoassay (Dubey, Herbert, Abbott & Martensz, 1984). The limit of sensitivity was 0-14 nmol/1; inter-and intra-assay coefficients of varia¬ tion were 14-8 and 7-8% respectively.…”

Section: Radioimmunoassaysmentioning

confidence: 99%

Naloxone-induced secretion of LH in the male Syrian hamster: modulation by photoperiod and gonadal steroids

Roberts¹,

Hastings²,

Martensz³

et al. 1985

The role of endogenous opiates in the regulation of photoperiodically induced testicular regression was studied in the male Syrian hamster. In reproductively active hamsters exposed to a long photoperiod (LD; 16 h light: 8 h darkness) or to short days (SD; 8 h light: 16 h darkness) for 20 weeks or to SD after pinealectomy, administration of naloxone, a competitive opiate receptor antagonist, at doses of 2.5-20 mg/kg, significantly increased serum LH concentrations. In marked contrast, these doses of naloxone did not produce any change in LH levels in reproductively quiescent hamsters exposed to SD for 8 weeks. The influence of gonadal steroids on the LH response to naloxone was studied in hamsters castrated or castrated and implanted s.c with a capsule containing testosterone. Naloxone did not induce LH release in castrated hamsters maintained in LD or in SD, but this response was restored in LD but not SD when serum testosterone concentrations were maintained at levels similar to those observed in intact reproductively active hamsters. These results show that inhibition of reproduction by the photoperiod prevents naloxone-induced LH release in the male hamster. This lack of response to naloxone is not due, however, to the lower testosterone titres present in these animals compared with reproductively active animals. Responsiveness to naloxone can be restored when the animal is rendered insensitive to the inhibitory photoperiod either by removal of the pineal gland or by induction of photorefractoriness by extended exposure to SD.

“…Its reported actions on behaviour (De Wied, 1977) may result from its breakdown in the blood, or secretion from the pituitary gland of smaller fragments which are behaviourally active and can be taken up by the brain (Mezey et al 1978). This study on ACTH, when compared with others on prolactin, growth hormone and luteinizing hormone (Belchetz et al 1982;Martensz & Herbert, 1982;Dubey et al 1983;Dubey, Herbert, Abbott & Martensz, 1984), suggests that mechanisms exist which permit selective entry of anterior pituitary hormones into the cerebral compart¬ ment.…”

Section: Discussionmentioning

confidence: 54%

Relationship between adrenocorticotrophin bioactivity in blood and cerebrospinal fluid of rhesus monkeys

Beckford¹,

Herbert²,

Jones³

et al. 1985

Adrenocorticotrophin levels, measured by a cytochemical bioassay, were determined in the plasma and cerebrospinal fluid (CSF) of adult female rhesus monkeys which were ovariectomized and receiving oestrogen replacement therapy. In control monkeys, ACTH bioactivity was found in both CSF (10.2 +/- 1.8 ng/l) and plasma (186 +/- 51 ng/l) in samples taken at 14.00 h (lights on: 07.00-19.00 h). Dexamethasone treatment (0.2 mg/kg) twice daily for 4 days suppressed plasma ACTH levels (52.8 +/- 25.2 ng/l) but had no effect on CSF levels (7.6 +/- 2.7 ng/l). Raising plasma ACTH, either by daily injections of a long-acting preparation of ACTH (1-24) for 6 days or by bilateral adrenalectomy (and subsequently with-drawing cortisol replacement therapy) also resulted in no detectable changes in ACTH levels in the CSF. A regression analysis between ACTH in the plasma and CSF from samples taken throughout the experiments showed no correlation. In contrast, measurement of ACTH by radioimmunoassay, whilst satisfactory for determination of this peptide in plasma, could not identify authentic ACTH in the CSF. It is concluded that bioactive ACTH does not enter the CSF in detectable quantities from either the peripheral vascular compartment or from the animal's own pituitary gland, and that reducing ACTH secretion from the pituitary also has no effect on levels of ACTH in the CSF. This is in marked contrast to other pituitary peptide hormones, including prolactin, which is secreted together with ACTH during 'stress' but which, unlike ACTH, enters the CSF relatively easily.