C-type natriuretic peptide as a new regulator of food intake and energy expenditure

The physiological implication of C-type natriuretic peptide (CNP) including energy metabolism has not been elucidated, because of markedly short stature in CNP-null mice. In the present study we analyzed food intake and energy expenditure of CNP-null mice with chondrocyte-targeted CNP expression (CNP-Tg/Nppc^-/- mice), in which marked skeletal dysplasia was rescued, to investigate the significance of CNP under minimal influences of skeletal phenotypes. In CNP-Tg/Nppc^-/- mice, body weight and body fat ratio were reduced by 24% and 32%, respectively, at 20 wk of age, and decreases of blood glucose levels during insulin tolerance tests were 2-fold exaggerated at 17 wk of age, as compared with CNP-Tg/Nppc^+/+ mice. Urinary noradrenalin excretion of CNP-Tg/Nppc^-/- mice was greater than that of CNP-Tg/Nppc^+/+ mice by 28%. In CNP-Tg/Nppc^-/- mice, rectal temperature at 1600 h was higher by 1.1 C, and uncoupling protein-1 mRNA expression in the brown adipose tissue was 2-fold increased, which was canceled by propranolol administration, as compared with CNP-Tg/Nppc^+/+ mice. Oxygen consumption was significantly increased in CNP-Tg/Nppc^-/- mice compared with that in CNP-Tg/Nppc^+/+ mice. Food intake of CNP-Tg/Nppc^-/- mice upon ad libitum feeding and refeeding after 48 h starvation were reduced by 21% and 61%, respectively, as compared with CNP-Tg/Nppc^+/+ mice. This study unveiled a new aspect of CNP as a molecule regulating food intake and energy expenditure. Further analyses on precise mechanisms of CNP actions would lead to the better understanding of the significance of the CNP/guanylyl cyclase-B system in food intake and energy expenditure.