Effect of light manipulation on ovarian activity and melatonin and prolactin secretion in the domestic cat

Ovarian activity was assessed by the determination of oestradiol-17 beta concentrations in plasma and indirectly by sexual interaction with a male. In one experiment, cats (N = 10) were studied initially for 50 days in a 14-h light (14L) regimen, then for 90 days in 24L (N = 6) or 8L (N = 4). At approximately 45 days after the onset of 24L, all animals had increased oestradiol-17 beta concentrations during waves of folliculogenesis compared to previous values obtained under 14L. The incidence of oestrous cycles decreased under 24L to 1 per month compared to 2 per month under 14L. In the 8L animals, oestrous cycle activity ceased immediately with the change from 14L to 8L. Oestradiol-17 beta concentrations were significantly lower during 8L than in interoestrus in the same animals under 14L. In a second experiment, ovaries and uteri were removed in the 3rd day of oestrus from animals in 24L and 14L photo-periods (N = 3 in each). The increased oestrogen production was associated with a 2-fold increase in the number of large, preovulatory follicles. Prolactin concentrations were significantly lower in animals in 24L than 14L during both oestrus and interoestrus as well as during oestrus compared to interoestrus during both 24L and 14L. Melatonin concentrations were significantly lower in animals in 24L than 14L during interoestrus. Prolactin values were significantly higher in 8L than in 14L and 24L. These results indicate that exposure of the cat to continuous light (24L) stimulated folliculogenesis while an 8L regimen inhibited folliculogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)