Role of NO on vasopressin and oxytocin release and blood pressure responses during osmotic stimulation in rats.
NG-nitro-L-arginine methyl ester (L-NAME, 250 micrograms/5 microliters), an inhibitor of nitric oxide (NO) synthase, or artificial cerebrospinal fluid (5 microliters) was administered intracerebroventricularly to conscious naive rats or to rats treated subcutaneously (15 microliters/kg) with NaCl (0.15, 0.45, or 1.0 M) or given a needle prick only. Intracerebroventricular injection of L-NAME increased plasma concentration of vasopressin (VP) and oxytocin (OT) in control naive rats, indicating that NO tonically inhibits basal secretion of both hormones during isosmotic isovolemic conditions. Osmotic stimulation with hypertonic saline (0.45 and 1.0 M NaCl) elevated plasma levels of both hormones as expected. Central blockade of NO synthase further enhanced secretion of OT during mild, but not strong, osmotic stimulation, whereas the high levels of VP remained unaffected by L-NAME. In animals treated with the needle prick or 0.15 M NaCl, only OT levels were increased after L-NAME. Therefore, NO selectively inhibits OT release in response to a painful stimulus (needle prick) and moderate osmotic stimulation to promote a preferential release of VP. A transient pressor response was observed after subcutaneous injection of 0.15 and 0.45 M NaCl, but a sustained response was obtained after 1.0 M NaCl. Regardless of whether the animals received NaCl solutions, however, treatment with L-NAME elevated blood pressure in all animals. Thus NO-induced vasodilation maintains basal arterial blood pressure and limits the pressor response to osmotic stimulation.
Kadekaro
M
M
Division of Neurosurgery, University of Texas Medical Branch at Galveston, 77555-0517, USA.
Liu
H
H
Terrell
M L
ML
Gestl
S
S
Bui
V
V
Summy-Long
J Y
JY
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology*; D007276:Injections, Intraventricular; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage / Q000494:pharmacology*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010121:Oxytocin / Q000097:blood / Q000378:metabolism*; D010812:Physical Stimulation; D011188:Potassium / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic / Q000494:pharmacology*; D012867:Skin; D012964:Sodium / Q000097:blood; D012965:Sodium Chloride / Q000494:pharmacology; D013997:Time Factors; D014667:Vasopressins / Q000097:blood / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000187:drug effects
D012462:Saline Solution, Hypertonic; D014667:Vasopressins; D009569:Nitric Oxide; D012965:Sodium Chloride; D010121:Oxytocin; D012964:Sodium; D019001:Nitric Oxide Synthase; D011188:Potassium; D019331:NG-Nitroarginine Methyl Ester