AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 1 275-R288, Copyright © 1997 by American Physiological Society
Osmoregulation of the magnocellular neuroendocrine system during lactation
J. Y. Summy-Long, S. Gestl, M. L. Terrell, G. Wolz and M. Kadekaro
Department of Pharmacology, M. S. Hershey Medical Center, Pennsylvania State University, Hershey 17033, USA. js12@email.psu.edu
Glucose utilization and Fos expression were used to compare responses of
cerebral structures involved in osmoregulation in virgin and lactating rats
given 0.15, 0.85, or 1.5 M NaCl subcutaneously. In virgin animals, glucose
utilization increased (P < 0.05) in the supraoptic nuclei (SON),
paraventricular nuclei (PVN), and neural lobe (NL) proportionally to the
osmotic stimulus (0.15 M NaCl < 0.85 M NaCl < 1.5 M NaCl), whereas
metabolism in the median preoptic nucleus (MPO) and median eminence (ME)
increased only after 1.5 M NaCl. In lactating rats, enhanced utilization of
glucose in response to osmotic stimulation was absent in the PVN (0.85 M
NaCl), MPO, and ME or significantly (P < 0.01) reduced (SON, PVN, NL)
compared with virgin animals. Glucose utilization in each structure
correlated linearly with plasma osmolality but with a lower slope (P <
0.05) in lactating animals. Magnocellular neurons expressing Fos in the SON
increased linearly with plasma osmolality and were more numerous (P <
0.05) in control lactating animals but increased less (P < 0.05) than in
virgin rats after 0.85 M NaCl. The attenuated magnocellular response during
lactation results from reduced afferent activation from osmosensitive
forebrain sites.
