Humoral pathway for local transfer of the priming pheromone androstenol from the nasal cavity to the brain and hypophysis in anaesthetized gilts

It is generally accepted that pheromones act by stimulating of the dendriti c receptors of the olfactory neurones massed in the olfactory epithelium. T his study was designed to ascertain whether it is possible for the boar phe romone androstenol (5 alpha -androst-16-en-3-ol) to be transported from the nasal cavity of anaesthetized gilts to the brain and hypophysis via local transfer from the blood in the perihypophyseal vascular complex. The experi ment was performed on days 18-21 of the porcine oestrous cycle (crossbred g ilts, n = 6). Tritiated androstenol (H-3-A; total amount 10(8) d.p.m. (758 ng)) was applied for 1 min onto the respiratory part of the nasal mucosa, 4 -6 cm from the opening of the nares. Arterial blood samples From the aorta and from the carotid rete were collected every 2 min during the 60 min peri od following administration of the steroid. Total radioactive venous efflue nt from the head was removed and an adequate volume of homologous blood was transfused into the heart through the carotid external vein. At the end of the experiment gilts were killed and tissue samples of the hypophysis and some brain structures were collected to measure radioactivity. In addition, corresponding control tissues were collected from three untreated gilts an d From three heads of gilts 60 min after H-3-A was applied post mortem into the nasal cavity. The concentration of H-3-A was significantly higher (P < 0.0001) in the arterial blood of the carotid rete than that of aorta. The mean rate of H-3-A counter current transfer from venous to arterial blood i n the perihypophyseal vascular complex, expressed as the ratio of the H-3-A concentration in arterial blood of the carotid rete to the H-3-A concentra tion in blood sampled simultaneously From the aorta, was 1.96 +/- 0.1. The concentration of H-3-A in plasma from the venous effluent from the head ran ged from 1.3 to 1.8 pg ml(-1). During the 60 min period of the experiment, 0.68% of the total applied dose of H-3-A was resorbed from the nasal cavity into the venous blood. Moreover, we found that H-3-A was present in the ol factory bulb (P < 0.01), amygdala, septum, hypothalamus, adenohypophysis, n enrohypophysis (P > 0.05) and perihypophyseal vascular complex (P < 0.01). These results demonstrate that, in anaesthetized gilts, the boar pheromone androstenol may be resorbed from the nasal mucosa, transferred in the perih ypophyseal vascular complex into arterial blood supplying the brain and hyp ophysis, and then arrested in the hypophysis and certain brain structures. We suggest that in addition to the standard neural pathway for signalling p heromones, another pathway exists whereby androstenol, as a priming pheromo ne, may be resorbed From the nasal cavity into the bloodstream and then pas s locally from the perihypophyseal vascular complex into the arterial blood supplying the brain and hypophysis, thus avoiding the first passage metabo lism in the liver.