Fasting-induced suppression of pulsatile luteinizing hormone secretion is related to body energy status in ovariectomized goats

Abstract

The effect of energy status on the response of luteinizing hormone (LH) pulse frequency to acute short-term energy deficiency created by fasting in estradiol-treated ovariectomized Shiba goats was studied in two experiments. In experiment 1, eight goats whose mean body weight (BW) was 25.6±5.8 (mean±S.D.) kg were fed 500 g hay cubes daily for 1 week. Then they were fasted for 3 days. Blood samples were collected for 4 h at 6 min intervals on the last day of feeding, first, second and third day of fasting for LH analysis. The goats were divided into light (<24 kg, n=4) and heavy (≥24 kg, n=4) groups for data analysis. There was no difference in LH pulse frequency between the last day of feeding and each day of fasting in the heavy group. LH pulse frequency was significantly ( P<0.05) suppressed on the second day (3.3±1.3 pulses/4 h) and on the third day (2.3±1.9 pulses/4 h) relative to the day prior to fasting (4.8±1.5 pulses/4 h) in the light group. In experiment 2, BW plus a body mass index (gBMI: (body weight (kg)/withers height (m)/body length (m)) × 10) were measured to define energy status. Nine goats (BW, 25.6±5.8 kg) were fed 500 g hay cubes daily for a week and then fasted for 3 days. Then they were divided into two groups offered either a maintenance ( n=4) or a restricted ( n=5) level of feeding for 4 weeks. The restricted level of feeding was 30% of maintenance requirement based on the BW recorded weekly. The feeding level was then adjusted to maintain BW for a further week followed by 3 day fasting for restricted animals. Blood samples were collected for 6 h at 10 min intervals on the day prior to fasting and on third day of fasting before and after the dietary manipulation. BW (26.6±2.2 to 26.8±3.8 kg) and gBMI (8.4±0.4 to 7.8±0.3) remained constant over the period prior to fasting for the maintenance animals but were significantly lower ( P<0.05) after 4 weeks for the restricted goats (BW, 26.3±2.1 to 21.5±2.4 kg; gBMI, 8.4±0.9 to 6.9±0.7). There was no significant difference in the LH pulse frequency between feeding and fasting day in both sampling periods in the maintenance group. In the restricted group, LH pulse frequency was not suppressed by fasting in the first sampling period (6.8±2.9 to 5.2±2.5 pulses/6 h), whereas it tended to be suppressed (4.8±3.1 to 1.6±2.3 pulses/6 h; P<0.06) and was significantly ( P<0.05) correlated to body weight ( r=0.70) and gBMI ( r=0.81) after the dietary manipulation. These results suggest that the suppressive effect of short-term energy restriction (fasting) on pulsatile LH secretion is related to body energy status.