Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated from ovine hypothalamus as two molecular forms, the basic 38 residue amidated peptide PACAP-38 and the N-terminal 27 amino acid sequence PACAP-27. A dense plexus of PACAP immunoreactive fibres is present in the internal and external layers of the median eminence and in other parts of the hypothalamus with PACAP cell bodies in the paraventricular and supraoptic nuclei. The present study shows, for the first time, that, as assessed by radioimmunoassay of extracted plasma, the amount of PACAP-38 in hypophysial portal is significantly greater than in peripheral blood, and that as assessed by reversed phase high performance liquid chromatography, PACAP 1-38 is the major form in portal blood. This evidence is crucial for the fact that PACAP-38 may be a hypothalamic-pituitary regulatory factor.

SUMMARY1. An operation on dogs for the implantation ofguide tubes to the lateral ventricle and cisterna magna and a method whereby the ventricular space can be repeatedly perfused in conscious and unrestrained animals are described.2. The characteristics of a recirculatory perfusion system were examined and the bulk formation and absorption of cerebrospinal fluid and the volume of the ventricular space perfused were derived from the concentrations achieved during the infusion of inulin into the system. 3. 5-hydroxyindol-3-ylacetic acid (5-HIAA), the acid metabolite of 5-hydroxytryptamine, and 3-methoxy-4-hydroxyphenylacetic acid (HVA), the main acid metabolite of dopamine, were demonstrated to be mainly removed from cerebrospinal fluid (c.s.f.) by an active transport system localized in the region of the fourth ventricle. 4. It was possible to inhibit the active transport of these acids from cerebrospinal fluid by pre-treating the dogs with probenecid.

The steroid anaesthetic Althesin (Glaxo), which is a mixture of two C21 steroids, alphaxalone (3 alpha-hydroxy-5 alpha-pregnane-11, 20-dione--the active compound) and alphadolone acetate (21-acetoxy-3 alpha-hydroxy-5 alpha-pregnane-11, 20-dione), has been especially useful for the study of forebrain-autonomic and neuroendocrine functions. As determined by the loss of the righting reflex, Child et al. found no sex difference in the anaesthetic dose of Althesin administered intravenously (i.v.). However, in our neuroendocrine studies in which the anaesthetic was administered intraperitoneally (i.p.) and at dosage sufficient to produce surgical anaesthesia and analgesia, we observed a sex difference in the efficacy of Althesin. This may explain the difficulties that have been encountered in obtaining adequate anaesthesia (blockade of the somatomotor response to pain) with Althesin. Here we report, using cortical electroencephalography, that Althesin is a more potent anaesthetic than either sodium pentobarbitone or urethane, and that anaesthesia in the male rat requires about four times more Althesin (administered i.p.) than in the female. This sex difference is age dependent, can be abolished by administering oestrogen to the male, does not depend on sexual differentiation of the brain, and cannot be attributed to a sex difference in the metabolic clearance rate of alphaxolone. These results, taken together with those of Richards and Hesketh, suggest that the effect of alphaxalone may be mediated by interactions with synaptic membranes that are more specific than simply a generalized change in membrane structure, and that these interactions are affected by sex steroids.

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The concentrations of endogenous γ-aminobutyric acid (GABA) receptor ligands were measured in hypophysial portal plasma by a sensitive and specific radioreceptor assay. Portal plasma contained higher concentrations of GABA receptor ligands than peripheral controls, although this increase was not due to authentic GABA but an unknown low-affinity ligand. Evidence is presented to support the hypothesis that the dipeptide homocarnosine may represent at least a part of this unknown. Electrical stimulation of median eminence evoked a massive (7.8-fold) increase in the rate of release of GABA (but not the low-affinity component) into portal blood. These results suggest that GABA and possibly other low-affinity ligands such as homocarnosine could serve as factors involved in the central control of anterior pituitary function.

The purpose of this study was to compare the control of adrenocorticotropin (ACTH) and corticosterone secretion in homozygous Brattleboro rats with their syngeneic controls, Long-Evans rats, and with rats of the Wistar strain. Plasma concentrations of ACTH and corticosterone were measured by radioimmunoassay in trunk blood, and corticotropin-releasing factor 41 (CRF-41), arginine vasopressin (AVP), and oxytocin were assayed in hypophysial portal vessel blood. Portal plasma was extracted with methanol for CRF-41 determination, and four different antisera and several different high-performance liquid chromatography (HPLC) systems were used to investigate AVP release. The peripheral plasma concentrations of ACTH and corticosterone were significantly higher in Long-Evans and homozygous Brattleboro than in Wistar rats. This difference was due, at least in part, to an approximately twofold greater release of CRF-41 into hypophysial portal blood of the Long-Evans and Brattleboro compared with Wistar rats. There was no significant difference between the strains in the output of oxytocin into portal blood. While no AVP could be detected in the neural lobe of homozygous Brattleboro rats, a small amount of AVP-like immunoreactivity was detected in unextracted hypophysial portal blood from homozygous Brattleboro rats. However, this AVP-like immunoreactivity was clearly distinct from authentic AVP in several HPLC systems, had no antidiuretic activity, and on gel filtration had a relative molecular mass greater than 5 kD. In contrast, the AVP-like immunoreactivity in hypophysial portal blood from Long-Evans rats co-eluted with authentic AVP in all HPLC systems tested. These findings show that in the homozygous Brattleboro rat authentic AVP is not released into hypophysial portal blood and that, therefore, the normal plasma concentrations of ACTH in this mutant are maintained by CRF-41 and possibly other hypothalamic and/or pituitary factors which facilitate ACTH release.

The concentrations of dopamine, noradrenaline and their respective primary neuronal metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylethyleneglycol (DHPG) were measured in the hypophysial portal and peripheral plasma of sheep and rats by combined gas chromatography-mass spectrometry. Hypophysial portal and jugular blood samples were taken at 5- to 10-min intervals for 3-7 h from six conscious ovariectomized ewes. Blood was also collected for 30 min under urethane anaesthesia from the cut pituitary stalk from 16 pro-oestrous female and five intact male rats. In ovariectomized ewes, noradrenaline concentrations were higher in hypophysial portal plasma than in peripheral plasma (6.6 +/- 0.8 vs 2.2 +/- 0.4 nmol/l). In contrast, dopamine was undetectable (less than 1 nmol/l) in the portal and peripheral plasma of all ewes. Plasma levels of DOPAC and DHPG in portal and jugular samples were similar. In all pro-oestrous female rats, plasma concentrations of dopamine were higher in portal blood than in jugular blood (8.0 +/- 1.4 vs 4.8 +/- 0.6 nmol/l). Detectable concentrations of dopamine were measured in the portal plasma of two out of five male rats. Noradrenaline concentrations were higher in portal plasma than in peripheral plasma of both female (8.3 +/- 1.7 vs 3.7 +/- 0.6 nmol/l) and male (14.8 +/- 2.7 vs 6.1 +/- 1.2 nmol/l) rats. These data show that noradrenaline, but not dopamine, is secreted into the long portal vessels in sheep. The results suggest that there are species differences in the secretion of hypothalamic dopamine into hypophysial portal blood.