Substance P (SP) has been shown to be present in the hypothalamus and anterior pituitary. To evaluate a possible physiological role of endogenous SP in the control of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release, specific antiserum against SP (anti-SP) was injected intraventricularly (3 µl into the third ventricle) or intravenously (50 or 200 µl) into conscious, ovariectomized (OVX) rats. Third ventricular injection of the antiserum induced a significant decrease in both plasma LH and FSH levels when compared to values in control animals injected with normal rabbit serum (p < 0.01 and p < 0.025, respectively). The effect was observed within 10 min and levels remained suppressed for 60 min. In contrast, intravenous injection of large doses of anti-SP had no effect on the release of both hormones. In order to confirm the stimulatory effect of SP itself, synthetic SP was injected intravenously and intraventricularly into estrogen-primed (E-primed), OVX rats. Synthetic SP dramatically stimulated LH release, but not FSH release when injected either intravenously or intraventricularly at doses of 10 and 50 µg (p < 0.001, p < 0.005 vs. control, respectively). To investigate any direct action of SP on gonadotropin release from the anterior pituitary gland, synthetic SP was incubated with dispersed anterior piutitary cells harvested from E-primed OVX rats. SP did not affect the release of gonadotropins in vitro. These results indicate that endogenous hypothalamic SP exerts a tonic stimulatory hypothalamic control of basal gonadotropin release in OVX rats.

To evaluate a possible physiological role of endogenous substance P (SP) in the control of growth hormone (GH; somatotropin) secretion, a specific antiserum against SP (anti-SP) was injected intraventricularly (3 I1 into the third cerebral ventricle) in unanesthetized unrestrained normal male rats. Control rats received an equivalent volume of normal rabbit serum (NRS). Intraventricular iniection of the NRS lowered plasma GH concentrations significantly. The lowering was detected on first measurement at 10 min after injection and was maximal at 30 min. This was followed by a return toward the initial levels. Third ventricular injection of antiserum significantly increased plasma GH in comparison with control animals injected with NRS. The effect was observed within 10-20 min, and levels remained elevated for the 120-min duration of the experiment. To confirm the possible inhibitory role of endogenous SP on GH release, 3 pl of 0.9% NaCl (saline) alone or saline containing a specific antagonist of SP, was injected into the third ventricle of normal male rats. The antagonist also increased plasma GH sigicantly (P < 0.005) within 5 min compared with values in the saline-injected control group. Levels remained elevated for 30 min but had returned toward control values 60 min after injection. In contrast, synthetic SP significantly decreased plasma GH when injected intravenously or intraventricularly compared with plasma GH in the control saline-injected group.To investigate a possible direct action of SP on GH release from the anterior pituitary gland, we incubated synthetic SP with dispersed anterior pituitary cells for 1 hr. The release of GH from incubated anterior pituitary cells was not affected at any dose of SP (10-' to 10-6 M) tested. These data strongly indicate that endogenous SP has a physiological inhibitory role in the control of GH secretion at the level of the hypothalamus in the male rat. Substance P (SP) was originally detected in equine brain and intestine by Von Euler and Gaddum in 1931 (1). This undecapeptide was isolated from the hypothalamus and characterized by Leeman in 1970-1971 (2, 3). Immunocytochemical studies have demonstrated an SP-containing neuronal system in the hypothalamus (4-10), and the peptide has been localized to cells of the anterior pituitary gland as well (11,12 In Vivo Experiments. Experiment I. Six to 8 days before the experiment, a 23-gauge stainless steel cannula (17 mm in length) was implanted into the 3V as described earlier (13). Each cannula was provided with a mandril to prevent its obstruction. The location of the cannula in the 3V was confirmed when cerebrospinal fluid flowed continuously from the cannula. After implantation, the animals were placed in individual cages until the day of the experiment. Twenty-four hours prior to the experiment, an indwelling catheter was inserted into the right jugular vein by using the technique of Harms and Ojeda (14) while the animal was Abbreviations: SP, substance P; GH, growth hormone; GHRH, GH-releasing hormone; ...