Cyclic GMP may potentiate lordosis behaviour by progesterone receptor activation.
The purpose of this study was to test the hypothesis that cGMP acts as a progesterone substitute to facilitate lordosis in oestrogen-primed rats. Female Sprague-Dawley rats underwent stereotaxic surgery to place a 26-gauge guide cannula into the third ventricle. Bilateral ovariectomy was done at the same time as stereotaxic surgery. Five days later ovariectomized rats were primed with 2 microg estradiol benzoate 24 and 48 h prior to behaviour testing. Some animals were further injected with 200 microg progesterone 4 h before behaviour testing. A nitric oxide synthase inhibitor infused into the third ventricle before progesterone administration significantly reduced lordosis performance. 8-Bromo-cGMP, a cell permeable cGMP analogue, or saline vehicle was infused into the third ventricle of hormone-primed animals approximately 4 h prior to the first of 3-h behaviour tests. This cGMP analogue facilitated lordosis behaviour. We next used KT5823, a highly specific inhibitor of protein kinase G (PKG), to test the hypothesis that cGMP action is mediated by this kinase. In this experiment, KT5823 was infused 15 min before progesterone. KT5823 significantly decreased lordosis behaviour. RU486, a progesterone receptor antagonist, was used to assess whether the stimulatory effects of cGMP are mediated through the progesterone receptor. Oestrogen-primed animals were injected with 5 mg of RU486 or vehicle 60 min before infusion with 8-bromo-cGMP. RU486 significantly attenuated cGMP-facilitated lordosis behaviour. These data show that cGMP facilitates lordosis through activation of PKG and the progesterone receptor.
Chu
H P
HP
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Morales
J C
JC
Etgen
A M
AM
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D002227:Carbazoles; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D006727:Hormone Antagonists / Q000494:pharmacology; D007211:Indoles; D015735:Mifepristone / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D011187:Posture / Q000502:physiology*; D011374:Progesterone / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011980:Receptors, Progesterone / Q000378:metabolism*; D012726:Sexual Behavior, Animal / Q000187:drug effects / Q000502:physiology*
D000470:Alkaloids; D002227:Carbazoles; D004791:Enzyme Inhibitors; D004967:Estrogens; D006727:Hormone Antagonists; D007211:Indoles; D011980:Receptors, Progesterone; C073601:KT 5823; C016276:8-bromocyclic GMP; D015735:Mifepristone; D011374:Progesterone; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester