Prolactin stimulates dopamine release from male but not from female rat striatal tissue superfused in vitro

Direct prolactin (PRL) effects on dopamine (DA) release from fragments of rat striatal tissues were studied by the in vitro superfusion technique. The DA collected in the superfusates was quantified by a radio-enzymatic assay. In the present experiments, intact and one-week gonadectomized adult male and female rats were used. The spontaneous release of DA from male and female rat striatal tissues was relatively stable after a 60 min equilibration period. The basal release rate of DA from striatal tissues from intact males infused only with medium over a 76 min period was 22.5 +/- 0.7 pg/mg/min (X +/- SE of 4 experiments). Infusion of highly purified PRL (NIAMDD-rPRL-I-5) at a concentration of 1 microgram/ml for 24 min significantly augmented DA release from striatal tissues from intact and castrated males (167 +/- 15% (n=6) and 203 +/- 32% (n=4), respectively) over pre-infusion basal levels. Infusion with heat-denatured PRL or other proteins had no effect on DA release from intact male striatal tissues. In parallel experiments, infusion of PRL at 0.1, 1 or 10 micrograms/ml concentrations for 24 min had no effect on the basal release of DA from striatal tissues from intact and ovariectomized females. These results demonstrate that an absolute sexual difference exists in the responsiveness of rat striatal tissues to PRL infused in vitro. Interestingly, this sexual difference was not modified by short-term castration.

Production and characterization of antisera to synthetic thyrotropin-releasing hormone (TRH)

To generate anti-thyrotropin-releasing hormone (TRH) antibodies TRH was rendered antigenic presumably by reaction of its histidine residue with bis-diazotized benzidine (BDB) coupled to bovine serum albumin (BSA). Six California white rabbits were each injected with 330 micrograms protein/ml of emulsified immunogen by the multisite intradermal immunization technique. Seven repeated injections were given at 30-day intervals using half of the original quantity of antigen. Antibodies binding 125I-TRH appeared in the serum of four of the six rabbits three months after the first injection. Five months later the sera of two rabbits bound 50% of the labeled TRH at 1:6000 final dilution. Using this antiserum a radioimmunoassay for TRH was developed in which as little as 10 pg/300 microliter unlabeled TRH can be detected. The linear range of detectable TRH was 10 to 10000 pg. No cross-reaction with various hypothalamic and pituitary hormones, neurotransmitters, neuropeptides, and BSA were detected in this immunoassay. Extracts from rat and frog hypothalami produced 125I-TRH-binding inhibition curves parallel to synthetic TRH. Samples from elutes of rat medio-basal hypothalami superfused in vitro were examined by using this antiserum. Serial dilution of superfusate showed a similar inhibitions curve. Stimulatory effect of K+ depolarization on TRH release from superfused hypothalami was inhibited in Ca2+-free ethylenediaminetetraacetic acid medium. Ouchterlony double diffusion test of the TRH antisera revealed that low levels of antibodies against albumin but not immunoglobulin G or ovalbumin were also produced. However, the immunoprecipitates could only be detected with undiluted serum. In conclusion, this antiserum generated one of the most sensitive TRH radioimmunoassay currently available in the literature. The anti-TRH serum produced by this method can be used to examine both content of TRH from several tissues as well as release from hypothalamic tissue in vitro and might be useful to trace brain TRH pathways by immunocytochemistry.