Effects of 5-hydroxytryptamine uptake blockers on the release of LH and prolactin in several different experimental steroid models in the rat

Abstract

The effect of the 5-hydroxytryptamine (5-HT) uptake blockers on the surges of LH and prolactin has been investigated in pro-oestrous rats and various experimental models used frequently to study the effects of steroids on LH and prolactin secretion in female rats. The steroid models were: rats ovariectomized on dioestrus, injected immediately with oestradiol benzoate (OB) and at 12.00 h on the next day (presumptive pro-oestrus) with progesterone (model 1); long-term ovariectomized rats injected with a single injection of OB and 72 h later with either progesterone (model 2) or OB (model 3); long-term ovariectomized rats injected daily with OB (model 4). The uptake blockers alaproclate (3-30 mg/kg) and zimelidine (20 mg/kg) were injected and blood samples withdrawn from previously implanted intra-atrial cannulae. Plasma LH and prolactin concentrations were determined by radioimmunoassay. The present study confirmed that a surge of LH occurs at about 17.00-18.00 h of the presumptive day of pro-oestrus in model 1, at about 5 h after (approximately 17.00 h) the injection of either progesterone or the second injection of OB in models 2 and 3, and diurnally in model 4, and the simultaneous occurrence of a prolactin surge in models 2 and 4. A surge of prolactin at the same time as the LH surge was shown to occur also in models 1 and 3. Alaproclate (30 mg/kg) administered at 15.00 h delayed significantly the peak of the prolactin surge in the pro-oestrous rat and models 1, 3 and 4, and in the latter the magnitude of the prolactin surge was also significantly reduced. By contrast, the peak of the prolactin surge in model 2 was significantly prolonged by alaproclate. Alaproclate had no significant effect on either the timing or the magnitude of the LH surge in the pro-oestrous rat, and models 3 and 4. The peak of the LH surge was delayed by alaproclate in model 1 and abolished in model 2, providing further evidence for the possible importance of interactions between 5-HT and progesterone in neuroendocrine control. Zimelidine had no significant effect on either the LH or prolactin surge in the pro-oestrous rat and in models 1 and 2. These results show that normal 5-HT uptake is necessary for the normal timing and/or magnitude of the spontaneous and steroid-induced prolactin surge but is not essential for the normal timing and magnitude of the spontaneous surge of LH and the LH surge in some but not all steroid models.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of antiserum to thyrotrophin-releasing hormone on the concentrations of plasma prolactin, thyrotrophin and LH in the pro-oestrous rat

“…The plasma concentrations of prolactin were measured using a double-antibody radioimmunoassay kit supplied by the NIADDK (Baltimore, MD, U.S.A.) as used in this laboratory by Horn & Fink (1985). Plasma concentrations of LH were measured by the ovine-ovine radioimmunoassay (Niswender, Midgley, Monroe & Reichert, 1968) as used in this laboratory (Horn & Fink, 1985). Plasma con¬ centrations of TSH were determined by doubleantibody radioimmunoassay using the kit supplied by the NIADDK and the results are expressed relative to the NIADDK rat TSH-RP-2 standard.…”

Effects of 5-hydroxytryptamine uptake blockers on the concentration in brain of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in male rats, pro-oestrous rats and ovariectomized rats treated with oestrogen and progesterone

“…Animals used in this series of experiments were male and female COB Wistar rats ( 180-250 g) maintained as described by Horn & Fink (1985). The experimental models studied were: (i) the male rat; (ii) the prooestrous female rat; (iii) the short-term ovariectomized rat treated with 20 pg OB and 2 mg progesterone (model 1 ; Horn & Fink, 1985); (iv) the long-term ovari¬ ectomized female rat treated with 20 pg OB and 2 mg progesterone (model 2; Horn & Fink, 1985).…”

“…The studies by Horn & Fink (1985) indicated that uptake blockade of 5-hydroxytryptamine (5-HT) can affect the release of luteinizing hormone (LH) and prolactin in pro-oestrous rats and in several different experimental animal models which have been used to study the effects of steroids on the release of LH and prolactin. The experiments reported in the present paper were carried out to determine whether the changes in hormone secretion did in fact reflect changes in 5-HT turnover in brain as indicated by the ratio of 5-hydroxyindoleacetic acid (5-HIAA)/5-HT (Tozer, Neff & Brodie, 1966).…”

“…Four types of animal model were studied: the male rat, the pro-oestrous female rat, rats ovariectomized on dioestrus and injected immediately with oestradiol benzoate (OB) followed by an injection of progest¬ erone on the next day (model 1; Fink, 1979;Horn & Fink, 1985), and long-term (3^weeks) ovariecto¬ mized rats injected with OB followed 72 h later by an injection of progesterone (model 2; Caligaris, Astrada & Taleisnik, 1968;Horn & Fink, 1985). Models 1 and 2 were chosen since there is increasing evidence for an interaction between 5-HT and progesterone in the control of neuroendocrine function (Munaro, 1978;Franks, McElhone, Young et al 1980;Walker, 1983;Walker & Wilson, 1983) whereas evidence for .a pos¬ sible interaction between oestrogen and 5-HT (models 3 and 4; Horn & Fink, 1985) is less convincing (Crowley, O'Donohue, Muth & Jacobowitz, 1979;Cone, Davis & Goy, 1981).…”

“…Models 1 and 2 were chosen since there is increasing evidence for an interaction between 5-HT and progesterone in the control of neuroendocrine function (Munaro, 1978;Franks, McElhone, Young et al 1980;Walker, 1983;Walker & Wilson, 1983) whereas evidence for .a pos¬ sible interaction between oestrogen and 5-HT (models 3 and 4; Horn & Fink, 1985) is less convincing (Crowley, O'Donohue, Muth & Jacobowitz, 1979;Cone, Davis & Goy, 1981).…”