Antiserum to prolactin lowers blood pressure (BP) in spontaneously hypertensive rats

Antisense inhibition of thyrotropin-releasing hormone reduces arterial blood pressure in spontaneously hypertensive rats

Thyrotropin-releasing hormone (TRH) plays an important role in central cardiovascular regulation. Recently, we described that the TRH precursor gene overexpression induces hypertension in the normal rat. In addition, we published that spontaneously hypertensive rats (SHR) have central extrahypothalamic TRH hyperactivity with increased TRH synthesis and release and an elevated TRH receptor number. In the present study, we report that intracerebroventricular antisense (AS) treatment with a phosphorothioate oligonucleotide against the TRH precursor gene significantly diminished up to 72 hours and in a dose-dependent manner the increased diencephalic TRH content, whereas normalized systolic blood pressure (SABP) was present in the SHR compared with Wistar-Kyoto (WKY) rats. Although basal thyrotropin was higher in SHR compared with WKY rats and this difference disappeared after antisense treatment, no differences were observed in plasma T4 or T3 between strains with or without AS treatment, indicating that the effect of the AS on SABP was independent of the thyroid status. Because the encephalic renin-angiotensin system seems to be crucial in the development and/or maintenance of hypertension in SHR, we investigated the effect of antisense inhibition of TRH on that system and found that TRH antisense treatment significantly diminished the elevated diencephalic angiotensin II (Ang II) content in the SHR without any effect in control animals, suggesting that the Ang II system is involved in the TRH cardiovascular effects. To summarize, the central TRH system seems to be involved in the etiopathogenesis of hypertension in this model of essential hypertension.

Prolactin regulation of tuberoinfundibular dopaminergic neurons: immunoneutralization studies

The purpose of this study was to determine the effects of acute hypoprolactinemia on tuberoinfundibular dopamine (DA) neurons using a rabbit anti-rat prolactin antiserum (PRL-AB) to immunoneutralize circulating prolactin under basal conditions and at various times after haloperidol-induced hyperprolactinemia. The specificity of PRL-AB for prolactin was determined by examining the ability of unlabelled hormone to displace binding of 125I-labelled prolactin to PRL-AB. Tuberoinfundibular DA neuronal activity was estimated by measuring the concentrations of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence which contains terminals of these neurons. Systemic (i.v.) administration of 200 microl of PRL-AB decreased plasma prolactin concentrations below detectable levels for at least 4 h, and this was accompanied by a pronounced decrease in DOPAC concentrations in the median eminence of females, but not males. Central (i.c.v.) administration of 2 microl PRL-AB diluted up to 1:100 mimicked the inhibitory effect of systemic administration of PRL-AB on median eminence DOPAC concentrations suggesting that the tonic stimulatory effect of prolactin on the basal activity of tuberoinfundibular DA neurons in females occurs via a central site of action. In male rats, blockade of anterior pituitary DA receptors with haloperidol (1 mg/kg; s.c.) caused an prompt (by 1 h) increase in plasma prolactin concentrations which was maintained for at least 12 h. Haloperidol-induced hyperprolactinemia also caused a delayed (at 6 and 12 h) increase in median eminence DOPAC concentrations in these animals which was blocked by PRL-AB. Exposure of rats to initial priming periods of endogenous hyperprolactinemia of up to 6 h duration (followed by 6 h or more of PRL-AB-induced hypoprolactinemia) failed to alter median eminence DOPAC concentrations unless prolactin exposure was reinstated by an i.c.v. injection of prolactin. These results confirm that prolactin mediates the stimulatory effects of haloperidol on tuberoinfundibular DA neurons, and reveal that delayed induced activation of these neurons by prolactin is dependent upon a priming period of sustained hyperprolactinemia longer than 3 h for initiation and maintenance of this response.

Interaction of prolactin with adrenal hormones in blood pressure regulation in rats

This study examined the role of the adrenals in the systolic blood pressure (BP) response to ovine prolactin (oPRL) administration as well as the interaction of oPRL with epinephrine (EPI), norepinephrine (NOR), and corticosterone (CORT) on BP in the rat. After intraperitoneal implantation of 7-day osmotic minipumps releasing 0.6 micrograms oPRL/h in 0.9% NaCl on day 1, BP was measured via tail cuff on days 1, 4, and 7 in adrenalectomized (ADX) and sham-ADX male rats (n = 8/group). BP was also measured in ADX rats receiving CORT (27.0 micrograms/h), EPI (1.7 micrograms/h), NOR (5.0 micrograms/h), CORT + oPRL, EPI + oPRL, and NOR + oPRL by osmotic pump (n = 8/group). All ADX rats not receiving CORT were given 1.0% NaCl replacement for drinking water. oPRL increased BP over 17 days in sham-ADX rats (P less than 0.01) but had no effect in ADX rats. BP also increased over 7 days in ADX animals receiving CORT, EPI (P less than 0.01), and NOR (P less than 0.01). BP responses to CORT + oPRL and EPI + oPRL were similar to those of CORT and EPI alone, respectively. However, the BP response to NOR + oPRL on day 4 was 250% (P less than 0.01) that to NOR alone and similar to NOR alone on day 7. Replacement of CORT + NOR + oPRL did not prolong the oPRL-induced sensitization to NOR. In no instance did oPRL, by itself, alter heart rate. These data suggest that the pressor response to oPRL requires the presence of the adrenal glands and that oPRL transiently potentiates the pressor response to NOR in vivo.