Nicotine alters the usual reciprocity between meal size and meal number infemale rat

Tobacco smoking reduces appetite and body weight (BW). Cessation of smoking leads to hyperphagia and weight gain. Daily food intake (FI) is a function of meal number (MN) and meal size (MZ), i.e., FI = MN x MZ. Under normal c onditions, the female Fischer rat has a periodic reciprocal fluctuation bet ween MZ and MN corresponding to phase of estrous cycle. Wide fluctuations b etween MZ and MN compensate each other to keep FI constant. Nicotine (5 mg/ kg BW/day) was infused via osmotic minipump for 7 days. Controls received s aline. Fl, MZ, and MN were measured by an Automated Computerized Rat Eater Meter. Nicotine significantly decreased BW and Fl via a decrease in MZ with out compensatory increase of MN. Nicotine cessation led to hyperphagia, nor malizing BW loss via an increase in MZ, which exceeded a compensatory decre ase in MN. Nicotine significantly prolonged the estrous cycle by an extensi on of proestrous phase. Nicotine significantly lengthened the intermeal int erval (IMI), delaying the start of the next meal and simultaneously decreas ing subsequent MZ. Stopping nicotine led to normalization of IMI and MZ. Da ta show that nicotine alters the usual reciprocal regulation between MZ and MN and leads to a prolongation of the estrous cycle. (C) 2001 Elsevier Sci ence Inc. All rights reserved.