Sexual dimorphism in relations of blood growth-hormone levels to body and brain weights in newborn rats.

The growth promoting effects of growth hormone (GH) are well-known. However, the studies in this respect did not consider the sexual dimorphism. The adverse--growth limiting--GH effects were also reported in human newborns (see Tan, 1992, 1995; Tan et al., 1998). A similar study was replicated in the newborn rat pups in the present work. The serum GH level, body weight, body height, right- and left-brain weights were measured just after birth in rat pups. The relations of the serum GH levels to the bodily measurements were found to be sexually dimorphic. Namely, there were no significant correlations between the serum GH levels and the body size (weight and height) in males, whereas there were inverse relations between these parameters in females. The GH level negatively linearly related to the right-, left-, and right- minus left-brain weights in females, whereas only the right-brain weight positively linearly correlated with the serum GH level, the right- minus left-brain weight being also positively linearly correlated with the serum GH level in males. The results suggested that the sexual dimorphism should be taken into consideration in studies concerning the global GH effects. The relation of the serum GH level to the right-left brain asymmetry, also sexually dimorphic, suggests a role of GH in cerebral lateralization.