Cavernous sinus and carotid rete of sheep and sows as a possible place for countercurrent exchange of some neuropeptides and steroid hormones

Comparison of the Rostral Epidural Rete Mirabile and the Patterns of Its Blood Supply in Selected Suiformes and Hippopotamuses

The rostral epidural rete mirabile (rete mirabile epidurale rostrale) is built of considerable small arterial vessels that anastomose with each other. This structure is formed as a result of the division of a large arterial vessel into many small arteries. Furthermore, on the other side of the rete mirabile, these small arteries are joined together to form one large artery, through which blood flows out of the rete mirabile. This system participates in decreasing the temperature of the brain and thus protects the body from thermal stress. Moreover, it influences body-water balance and has a crucial role in the retrograde transfer of neuropeptides. The goal of this study was to describe the rostral epidural rete mirabile and pathways that provide blood to this structure as well as compare it in selected Suiformes and hippopotamuses. The study was performed on desert warthogs (Phacochoerus aethiopicus), Eurasian wild boars (Sus scrofa), collared peccaries (Pecari tajacu), pygmy hippopotamuses (Choeropsis liberiensis), and common hippopotamuses (Hippopotamus amphibius). Preparations were made using the latex method and corrosion cast. An elongated shape characterizes its anatomy with a much wider rostral part than caudal part in the Eurasian wild boars, desert warthogs, and collared peccaries. The main source of blood was the branch to the rostral epidural rete mirabile branched off from the internal carotid artery. Moreover, blood enters the rete by the caudal branch and rostral branch to the rostral epidural rete mirabile. In hippopotamuses, the major source of blood was the rostral branches to the rostral epidural rete mirabile.

Hypophysial angiogenesis decodes annual time and underlies physiological adaptation to seasonal changes in the environment

Adaptation to annual changes in the environment is controlled by hypophysial hormones. In temperate zones, photoperiod is the primary external cue that regulates annual biological cycles and is translated by the pattern of melatonin secretion acting primarily in the hypophysial pars tuberalis. Angiogenic mechanisms within this tissue contribute to decode the melatonin signal through alternative splicing of the vascular endothelial growth factor A (VEGF-A) gene in both the pars tuberalis and the capillary loops of the infundibulum. The resulting melatonin-evoked differential productions of VEGF-A isoforms will induce seasonal remodeling of the vascular connection between the hypothalamus and hypophysis, and act as paracrine messengers in the pars distalis to generate the required seasonal endocrine response. Specifically, the long melatonin signal in winter upregulates antiangiogenic VEGF-A isoforms, which will reduce the number of vascular loops and the density of VEGF receptors in endocrine and folliculo-stellate (FS) cells, inhibit prolactin secretion, and stimulate FSH. In contrast, the short melatonin signal in summer upregulates proangiogenic VEGF-A isoforms that will increase the number of vascular loops and the density of VEGF receptors in endocrine and FS cells, stimulate prolactin secretion, and suppress FSH. A similar system has been identified in long day seasonal breeders, revealing that this is a conserved mechanism of adaptation across species. Thus, an angiogenesis-based, intrahypophysial system for annual time measurement controls local microvascular plasticity and conveys the photoperiodic signal readout from the melatonin sensitive pars tuberalis to the endocrine cells of the pars distalis to regulate seasonal adaptation to the environment.

The influence of steroids on noradrenaline-mediated contractile reactivity of the superficial nasal and facial veins in cycling gilts

The nasal venous blood may be directed through the facial vein into the systemic circulation or through the frontal vein into the venous cavernous sinus of the perihypophyseal vascular complex, where hormones and pheromones permeate from the venous blood into the arterial blood supplying the brain and hypophysis. The present study was designed to determine the effect of noradrenaline (NA) on the tension of the nasal, frontal and facial veins of cycling gilts, and influence of ovarian steroid hormones on NA-mediated contractile reactivity. Additionally, the enzyme dopamine-beta-hydroxylase catalysing the conversion of dopamine to noradrenaline (DbetaH) was immunolocalized in these vessels. Among three studied veins, the frontal proximal vein, that fulfill a key role in the supply of the nasal venous blood into the venous cavernous sinus, reacted to NA most strongly (P < 0.001) and this reaction was weaker in the periestrous period than in luteal phase (P < 0.001). Inversely, the reaction to NA of the facial proximal vein, that carry blood to the peripheral circulation, was stronger in the periestrous period than in luteal phase (P < 0.05). P4, E2 and T significantly lowered NA-mediated tension of the frontal proximal vein during the periestrous period (P < 0.001), while in the luteal phase P4 might antagonize relaxing effect of E2 to this vessel. The result suggests that supply of the nasal venous blood into the venous cavernous sinus is greater during the periestrous period than during the luteal phase. DbetaH was clearly expressed in the muscular layer of the isolated superficial nasal and facial veins of gilts in both studied stages of the estrous cycle. We suggest that the reactivity of the superficial veins of the nose and face to NA combined with the previously demonstrated reactivity of these veins to steroid ovarian hormones and male steroid pheromones may regulate the access of priming pheromone androstenol (resorebed in the nasal cavity) to the brain of gilts during periestrous period via humoral local destination transfer.

The influence of steroids on vascular tension of isolated superficial veins of the nose and face during the estrous cycle of gilts

The arrangement of the superficial facial veins enables blood flow from the nasal cavity into the peripheral circulation by two pathways: through the frontal vein into the cavernous sinus and through the facial vein into the external jugular vein. The current study was designed to determine whether estradiol and progesterone affect the vascular tone of the superficial veins of the nose and face in cycling gilts (Sus scrofa f. domestica) and to analyze the immunolocalization of progesterone receptors and estradiol receptors in these veins. The influence of hormones on vascular tension differed depending on the type of vessel and the phase of the estrous cycle. Estradiol decreased vascular tension in the nasal vein during the follicular phase (P<0.05) and increased tension in the frontal vein during the luteal phase (P<0.05). Progesterone increased the vascular tension of the frontal vein (P<0.05) and decreased the tension of the other veins (P<0.05) in both phases of the cycle. Expression of estradiol receptor beta but not of progesterone receptor was observed in the superficial veins of the nose and face. In conclusion, the effect of ovarian steroid hormones on the vascular tension of the superficial veins of the nose and face in female pigs as well as the reactivity of these veins to steroid boar pheromones can affect the blood supply from the nasal cavity to the venous cavernous sinus. We propose that the ovarian steroid hormones that modulate the vascular tension of the nasal and facial veins may also influence the action of boar pheromones absorbed into the nasal mucosa in gilts and may reach the brain via local destination transfer.

Humoral pathway for transfer of the boar pheromone, androstenol, from the nasal mucosa to the brain and hypophysis of gilts

Signaling and priming pheromones play an important role in intraspecies behavioral and sexual interactions and in the control of reproduction. It is generally accepted that pheromones act by stimulating the dendritic receptors in the mucus-imbedded cilia of olfactory neurons massed in the olfactory epithelium. The boar pheromone androstenol, known to induce sexual behavior in pigs, is 1 of 2 pheromones that have been chemically defined, tritiated and thus made available for use in studies. In Experiment 1, sexually mature cyclic gilts at Days 16 to 21 of the estrous cycle were humanely killed and the heads separated from the bodies. The heads were attached to a perfusion system using heated, oxygenated, heparinized, autologous blood. A total amount of 10(8) dpm (758 ng) of 3H-5 alpha-androstenol (3HA) was either infused into the angularis oculi veins that drain the nasal cavities (n = 7) over a 5-min period or applied through intranasal catheters onto the mucose surface (n = 16) for 2 min. In both groups frequent blood samples were collected from the carotid rete and from venous effluent. Concentration of 3HA in the arterial blood of the carotid rete after direct (into angularis oculi veins) or indirect (onto the nasal mucosa) administration of 3HA into veins draining the nasal cavities was significantly higher than background radioactivity before 3HA administration (P < 0.0001 and P < 0.05, respectively). The 3HA was selectively accumulated (compared with the respective control tissue) in the neurohypophysis (P < 0.001), adenohypophysis (P < 0.01), ventromedial hypothalamus (P < 0.05), corpus mammillare (P < 0.01), and perihypophyseal vascular complex (P < 0.001). In a second in vitro experiment, active uptake of 3HA into the nasal mucosa of the proximal, respiratory segment of the nasal cavity was observed. These results demonstrate a humoral pathway for the transfer of pheromones from the nasal cavity to the hypophysis and brain. Androstenol was taken up by the respiratory part of the nasal mucosa, resorbed into blood, transported to the cavernous sinus and transferred into the arterial blood of the carotid rete (supplying the hypophysis and brain), and then selectively accumulated in the hypophysis and certain brain structures.

The inhibitory effect of hCG on counter current transfer of GnRH and the presence of LH/hCG receptors in the perihypophyseal cavernous sinus--carotid rete vascular complex of ewes

The existence of the hormone passage from venous blood into arterial blood in the area of the perihypophyseal vascular complex has been demonstrated in some mammals, but its mechanism has not been defined. To study the regulatory mechanism we infused hCG into perihypophyseal cavernous sinus of ovariectomized, conscious ewes to test if the hCG would affect putative LH/hCG receptors and inhibit counter-current transfer of GnRH from the venous cavernous sinus to the arterial carotid rete. The latter study was done on an isolated head model. Ewes were ovariectomized in mid-anestrus and, after 4 to 5 wk were used in the experiments. On the day of experiment ewes were treated intramuscularly with estradiol benzoate or oil vehicle, and 18 to 20 h later were infused either with a multielectrolyte solution or hCG for 2 h via the venae angularis oculi. Immediately thereafter the ewes were anesthetized and exanguinated, and subsequently decapitated. The isolated head was perfused with Dextran in multielectrolyte. The 125I-GnRH was infused into the cavernous sinus via the venae angularis oculi for 5 min; contemporaneous samples were taken from the carotid rete and both jugular veins at 1-min intervals. Transfer of 125I-GnRH from the cavernous sinus to the carotid rete was inhibited by hCG in ewes pretreated with estradiol benzoate but not with oil (P<0.005). We collected tissue samples from the vascular complex of the cavernous sinus and carotid rete of cyclic ewes to determine the presence of LH/hCG receptors. In situ hybridization showed the presence of LH/hCG receptor mRNA transcripts in the walls of both arterial and venous compartments of the cavernous sinus-carotid rete complex, and immunohistochemistry revealed the presence of receptor proteins. These novel findings confirm previously obtained data suggesting that LH is a modulatory factor for the counter-current transfer of neuropeptides from the venous blood of the cavernous sinus to the arterial blood supplying the brain and hypophysis. The LH could modulate 125I-GnRH transfer acting directly on the vascular smooth muscle.

Cycle dependent variations in transfer of 133xenon from vagina to uterus in rats

The possible existence of an oestrus cycle dependent on local transfer of 133xenon from vagina to uterus was investigated in anaesthetized rats. 133Xenon in saline was infused into the vaginal lumen of rats in oestrous (n = 7) and dioestrous (n = 10). The uterus was removed 3 min after the infusion and the radioactivity in the organ counted, after which the remaining radioactivity in vagina was measured. The results showed that the radioactivity increased in all uteri compared with that of the background. The average transfer, expressed as per cent transfer, from vagina in the dioestrous group (5.5%) was significantly higher (P < 0.01, Mann-Whitney) than in the oestrous group (1.4%). The results suggest that the rate of transfer from vagina to uterus depended on the oestrous cycle. Vaginal treatment of women with progesterone for example, may similarly induce high local concentrations in the uterus. Empirically this is already used after in vitro fertilisation, it may also prevent progesterone induced migraine in menopausal women. The possible cycle dependent variations in the transfer in women should be evaluated.

Countercurrent transfer of 125I-LHRH in the perihypophyseal cavernous sinus-carotid rete vascular complex, demonstrated on isolated pig heads perfused with autologous blood

The objective of the study was to determine whether the local permeability of luteinizing hormone-releasing hormone (LHRH) from the venous blood of the perihypophyseal cavernous sinus into the arterial blood of the carotid rete, supplying the brain and hypophysis in gilts, depends on the day of the estrous cycle, as well as to determine whether this transfer exists when LH concentration in the blood is reduced (the experimental short-loop negative feedback for LH secretion after estradiol injection in ovariectomized gilts). Experiments were conducted on isolated gilt heads with necks, on chosen days of the estrous cycle (n = 40), and on previously ovariectomized gilts treated with estradiol benzoate (EB) (n = 5) or corn oil (n = 3). After exsanguination, the gilt heads with necks were disarticulated and about 30-45 min later were supplied with autologous, oxygenated, and heated blood at a stable blood flow and pressure through the left carotid artery for 30 min. 125I-LHRH was infused into both cavernous sinuses through the cannulated angularis oculi veins for 5 min. After 125I-LHRH infusion, radiolabeled LHRH was found (P < 0.001) in arterial blood taken from the carotid rete through the open right carotid artery in all animals used in the experiment: on Days 1-2 (six gilts), on Days 12-14 (seven gilts) of the estrous cycle, and in five ovariectomized gilts during negative feedback for LH surge (40 hr after EB). No significant radioactivity of 125I-LHRH was found in the arterial blood on Days 3-5 (n = 6), 9-11 (n = 4), and 15-21 (n = 17) of the estrous cycle. A very low level of radioactivity was found in the ovariectomized control group after the injection of corn oil (n = 3). These results provide evidence for the permeability of LHRH from the venous to the arterial blood and its retrograde transport with the arterial blood to the hypophysis and brain, after the ovulation period (Days 1-2) and on Days 12-14 of the estrous cycle. This suggests that a close relationship exists between the day of the estrous cycle and LHRH permeability from the venous to the arterial blood in the perihypophyseal cavernous sinus-the carotid rete complex in gilts-and that this mechanism may be included in a short-loop feedback for LHRH secretion.