Circadian rhythm in hypothalamic leptin receptor (Ob-Rb) mRNA expressions and cerebrospinal fluid and circulating glucose and leptin levels in lactating rats

Abstract

In lactating animals, the food consumption increases several-fold for milk supply to the pups. The present study was conducted to clarify the relationship between the hyperphagia during lactation and hypothalamic leptin receptor (Ob-Rb) mRNA expression, cerebrospinal fluid (CSF) and circulating leptin and glucose levels. Food intakes significantly higher in lactation than in non-lactation at all time points (3 points: light phase, 4 points: dark phase) of the day. However, the expression of the hypothalamic Ob-Rb mRNA showed similar circadian rhythms in both the non-lactation and lactation, with only slight differences between the two groups. CSF leptin and glucose levels were constant throughout the day in both non-lactation and lactation, and there was almost no difference between the two groups at each time point. Circulating leptin and glucose levels showed circadian rhythms only in the non-lactating period, and were lower in lactation than in non-lactation, especially in the dark phase. In conclusion, the present study provides evidence that Ob-Rb mRNA expression fluctuates in the lactation period as well as in the non-lactation period, suggesting that the expression profile of whole hypothalamic Ob-Rb may not contribute to the difference in food consumption between lactation and non-lactation, and that chronic decrease in blood glucose levels may be associated with the increase in food consumption during lactation.

Keywords: Cerebrospinal fluid; Food intake; Glucose; Lactation; Leptin; Receptor.

Fig. 1

Changes in dams (A): body weight, (B): food intake for 24 h, (C): plasma glucose levels, and (D): plasma leptin levels from pregnancy to lactation. The shaded band represents the pregnancy period. Values are the means and vertical lines represent the S.E.M. (n = 5). *P < 0.05 and **P < 0.01 vs. diestrus 2 (D2) rats.

Fig. 2

Circadian rhythm of (A): food intake, (B): CSF and blood glucose levels, (C): CSF and plasma leptin levels, and (D): hypothalamic OB-Rb mRNA expressions in non-lactation and day 10 of lactation. Shaded band represents the dark (light-off) phase. Values are the means and vertical lines represent the S.E.M. (n = 4–7/time point). Dissimilar superscripts denote significant differences (non-lactation; a,b, and c P < 0.05, lactation; A,B,C, and D P < 0.05). *P < 0.05 and **P < 0.01 vs. non-lactation at the same time.