Prolactin inhibition in lactating rats changes leptin transfer through the milk

Malnutrition during lactation reduces milk production and changes pup's leptin serum levels. To test prolactin role in this nutritional state, we evaluated whether prolactin suppression during lactation changes serum leptin in dams, its transfer through the milk, and pup's serum leptin. Lactating rats were treated with bromocryptine (1 mg/twice a day, sc) or saline three days before sacrifice (days 2 - 4 or days 19 - 21). Food intake and body weight were measured until sacrifice (4(th) and 21(st) day). Serum prolactin and leptin were determined by radioimmunoassay. Bromocryptine injected dams had lower serum prolactin and milk production as expected. The mothers presented lower food ingestion (day 21: - 25 %), lower body weight (day 4: - 12 %; day 21: - 10 %), higher serum leptin (day 4: + 68 %), lower milk leptin on the 4(th) day (11 times) and higher (8 times) on the 21(st) day. The offspring of bromocryptine-treated mothers presented lower body weight in both periods of lactation and lower serum leptin on the 4(th) day (-40%) and higher on the 21(st) day (+ 37%) of lactation. We suggest that prolactin, through its effect on leptin secretion into the milk, may play an important role in signalizing maternal nutritional status to the pups.