Jy. Summylong et al., EFFECTS OF CENTRAL INJECTION OF KYOTORPHIN AND L-ARGININE ON OXYTOCINAND VASOPRESSIN RELEASE AND BLOOD-PRESSURE IN CONSCIOUS RATS, Brain research bulletin, 45(4), 1998, pp. 395-403
Intracerebroventricular (ICV) administration of an inhibitor of nitric
oxide synthase (NOS) increases oxytocin but not vasopressin secretion
, in dehydrated rats [38], Surprisingly, central injection of L-argini
ne, the substrate for NOS, caused a similar effect, Kyotorphin (L-tyro
syl-L-arginine), a dipeptide formed from L-arginine by kyotorphin synt
hetase in the brain may mediate this magnocellular response, Therefore
, the dose and time responses of hormone release were compared followi
ng ICV injection of kyotorphin and L-arginine to conscious rats that w
ere normally hydrated or deprived of water for 24 h, In water-sated ra
ts, both L-arginine and kyotorphin increased blood pressure and plasma
glucose levels coincident with elevating circulating levels of oxytoc
in, but not vasopressin, In dehydrated animals, both L-arginine and ky
otorphin increased plasma oxytocin levels with a similar time course b
ut only kyotorphin decreased vasopressin release, D-arginine, like L-a
rginine, stimulated secretion of oxytocin, indicating a nonstereospeci
fic effect, A kyotorphin receptor antagonist (L-leucyl-L-arginine) giv
en ICV to dehydrated animals elevated plasma oxytocin and prevented th
e decrease in vasopressin levels after kyotorphin, Thus, kyotorphin, b
ut not L-arginine, appears to attenuate release of vasopressin either
directly from magnocellular neurons or indirectly via modulating compe
nsatory reflexes activated by the presser response. On the other hand,
an excess of L-arginine and kyotorphin within the CNS may mimic the s
tress response by augmenting release of oxytocin and activating the sy
mpathetic nervous system to increase blood pressure and plasma glucose
levels. (C) 1998 Elsevier Science Inc.