Local transfer of testosterone and aromatase activity in the spermatic cord in wild boar/pig hybrids in short-daylight and long-daylight periods.

The local transfer of testosterone (T) and immunolocalization of cytochrome P450 aromatase (P450arom) in the spermatic cord vessels of ten male wild boar×domestic pig hybrids were examined in December (short-daylight period) and June (long-daylight period). Total T concentration was determined in the jugular vein (JV) and free T concentration was estimated in the common carotid artery (CA), branches of the testicular artery supplying the testis (TA) and epididymis (EA), as well as in testicular veins draining blood from the testis (TV) and spermatic cord (SV). P450arom was immunolocalized in the arterial and venous vessels of the spermatic cord. The concentrations of total T in the JV and free T in the CA did not differ between the examined periods. However, in December, free T concentrations in the TA and EA were higher (p<0.01-0.001) than in the CA. In June, free T concentration was higher (p<0.01) in EA than in CA and TA. The concentrations of free T in the TV and SV were higher (p<0.001) than in the JV regardless of the period. Also, free T concentration in the SV was higher (p<0.05) in June than in December. P450arom was expressed in all layers of the arterial and venous vessels of the spermatic cord. In June, the intensity of the P450arom staining was higher than in December. The results suggest that the local supply of the male reproductive organs with steroid hormones operate in the hybrids of wild boar×domestic pig. This supply includes the local transfer of testosterone and the P450arom action.

Advances in understanding the physiological mechanism of maternal immune tolerance to the embryo.

The results of immunological studies, especially research conducted in the last decade, have shown that free (not bound to protein) progesterone molecules (fP(4)) can block the ability of dendritic cells, monocytes and macrophages to present antigens to Th cells and thereby reduce maternal immune activity and increase the maternal tolerance to the semiallogenic embryo. Endocrine studies have shown that fP(4) in the female reproductive organs are transferred at high concentrations into the arterial blood that supplies the oviduct and uterus due to the special adaptations of the blood circulation and lymph flow. Here, the authors present the results of numerous studies documenting their thesis that an important element of maternal tolerance of the semiallogenic embryo in the uterus is conditioned by the close interaction of two processes that occur in the reproductive organs: (1) the local decrease of maternal immune system activity, in which the ability of dendritic cells, macrophages and monocytes to present embryonic antigens to Th cells is blocked by fP(4); and (2) the proper function of the system governing the local retrograde and destination transfer of hormones, which increases the concentration of fP(4) that are able to immediately bind to their receptors in dendritic cells and in the monocytes and macrophages present in the blood supplying the oviduct and uterus. The authors believe that the local interaction of the immune and endocrine systems in the female reproductive tract reduces local maternal immunoreactivity and thus fulfils a critical physiological role; this mechanism protects the embryo but does not change the general immunological resistance of the mother.

Local effect of progesterone infusion into the porcine ovarian artery on androgen and estrogen secretion during the middle luteal phase.

The present study was undertaken to elucidate whether an increased, but physiological, amount of progesterone (P(4)) supplied to the porcine corpus luteum (CL) affects luteal secretion of androgens and estrogens in freely moving gilts. On day 9 of the estrous cycle, the jugular veins as well as both ovarian arteries and both ovarian veins of gilts were cannulated. Progesterone was infused into the right ovarian arteries of experimental gilts (n=5) on days 10, 11 and 12 of the estrous cycle at a rate adequate to physiological retrograde transfer found during the middle luteal phase of the cycle. The left ovarian arteries of the experimental gilts were infused with saline. Both ovarian arteries of the control gilts (n=5) were infused with saline. The P(4) infusion rate was 0.62 microg/min (10 day), 2x0.62 microg/min (11 day) and 3x0.62 microg/min (12 day). Blood samples were collected from the jugular vein and both ovarian veins of the experimental and control gilts on days 10-12 of the estrous cycle before and after P(4) or saline infusion. The mean plasma androstenedione (A(4)) level in the ovarian vein ipsilateral to the P(4)-infused ovary was higher (p<0.01) on days 10-12 of the estrous cycle than those found in the contralateral ovarian vein of the experimental gilts as well as the control gilts. The ovarian venous level of testosterone (T) in the ovarian vein ipsilateral to the P(4)-infused ovary on days 10-12 of the estrous cycle was not significantly different (p>0.05) from those found in the contralateral ovarian vein of the experimental gilts and ovarian vein of the control gilts. However, on day 12, a decrease in T concentration was demonstrated in the ovarian vein ipsilateral to the P4-infused ovary in comparison to those of the contralateral and control ovarian veins. The mean plasma 17beta-estradiol (E(2)) level in the ovarian vein ipsilateral to the P(4)-infused ovary was lower on days 10-12 than those found in the contralateral ovarian vein of the experimental gilts and in the ovarian vein of the control gilts (p<0.001). The results of the present paper indicate that local elevation of P4 concentration in blood supplying the ovary during the middle luteal phase of the porcine estrous cycle affected local secretion of androgens and estrogens. The effect of P(4) on the secretion of androgens and estrogens suggested the existence of a short regulatory loop of a positive feedback for A(4) secretion and a negative feedback for E(2) secretion.

The effect of unilateral progesterone infusion into the ovarian artery during the middle luteal phase on progesterone secretion in gilts.

The aim of the study was to determine, in an experiment performed on conscious gilts, whether an increased amount of progesterone (P4) supplied to the porcine corpus luteum (CL), maintained within a physiological systemic concentration would influence its own secretion. On day 9 of the estrous cycle the jugular veins as well as both ovarian arteries and both ovarian veins were cannulated. In the experimental gilts (n=5), P4 was infused into the right ovarian arteries on days 10, 11 and 12 of the estrous cycle at a rate adequate for physiological retrograde transfer found during the middle luteal phase. The left ovarian arteries of these gilts were infused with saline. Both ovarian arteries of the control gilts (n=5) were infused with saline. The P4 infusion rate was 0.62 microg/min (10 day), 2 x 0.62 microg/min ( 11 day) and 3 x 0.62 microg/min (12 day) and physiological levels of the steroid were maintained. Blood samples were collected from the jugular vein and both ovarian veins in the experimental and control animals on days 10, 11 and 12 of the estrous cycle during two periods on each day: before and after P4 or saline infusion. The mean plasma P4 level in the ovarian vein ipsilateral to the P4-infused ovary was significantly (p<0.001) higher on days 10-12 of the estrous cycle than those found in contralateral ovarian vein of the experimental gilts and in the ovarian vein of the control gilts. This was also true for day 12 of the estrous cycle (p<0.001). However, on days 10 and 11 plasma P4 in the vein from the P4-infused ovary tended (p<0.061) to be higher than those in veins from the saline-treated ovaries. The mean P4 concentration in the ovarian vein ipsilateral to the P4-infused ovary did not vary significantly (p>0.05) among the particular days of the experiment. In contrast, mean P4 levels in the contralateral ovarian vein of the experimental gilts as well as in the ovarian vein of the control gilts tended to decrease (p<0.06) between day 10 and day 12. The results of the present paper indicate that during the middle luteal phase of the porcine estrous cycle (days 10-12), ovarian P4 secretion remained unaltered due to the elevation of P4 concentration in blood supplying the steroid-infused ovary, while a decrease in P4 concentration was observed in ovarian veins of the saline-infused ovaries. The influence of the progestagen on its own secretion suggests that on days 10-12 of the porcine estrous cycle there is a short regulatory loop of positive feedback between P4 being retrograde transferred into the ovary and P4 ovarian secretion.

Luteinising hormone attenuates the vascular response to norepinephrine.

The present study examines the direct effect of luteinising hormone (LH) on the reactivity of the porcine uterine artery to norepinephrine (NE). Three-mm-long arterial segments collected during the luteal phase of the oestrous cycle were mounted in an organ bath for isometric tension recording. After 30 min of equilibration in optimal passive tone, one part of the vessels was treated with 10 ng/ml of LH in PBS (experimental), while a second part of the arterial segments was treated with 10 ng/ml of bovine serum albumin (BSA) in PBS (control). After 30 min of equilibration, NE was given to each organ bath in a cumulative concentration manner, ranging between 1 x 10(-8) mol/l to 3 x 10(-4) mol/l. NE caused a dose-dependent contraction of all experimental and control arteries. The addition of LH caused a rightward shift of the dose-response curve to NE. The corresponding EC50 values were 2.17 (+/- 0.39) micromol/l in PBS-pretreated vessels and 3.35 (+/- 0.41) micromol/l in LH-pretreated vessels (P < 0.05). The results of the present study demonstrate that LH attenuates the vascular response to NE in third-order branches of the uterine artery. Therefore, it can be suggested that besides the known effect of LH-hCG on the formation of vasoactive eicosanoids, an additional mechanism is involved in the direct action of LH on blood flow in the uterine arteries in pigs.

Retrograde transfer of testosterone to the porcine ovary in follicular and luteal phase of the estrous cycle in vivo.

This study was designed to determine the efficiency and rate of testosterone (T) retrograde transfer during the follicular and luteal phase of the estrous cycle in gilts (n=27). The efficiency and the rate of the retrograde transfer of T from the ovarian effluent into blood supplying the ovary were determined for the first time under in vivo conditions. Ovarian arterial blood concentration of T was higher than that in systemic blood during both, the follicular phase (p<0.01) and luteal phase (p<0.0001). The efficiency of the retrograde transfer of T into ovarian arterial blood was not dependent on concentration of testosterone in the ovarian venous blood. However, the efficiency and the rate of the retrograde transfer of T differed between phases of the estrous cycle. The presented results suggest that local retrograde transfer enriched the porcine ovary with an additional amount of T which may affect the ovarian secretory function.

Retrograde and local destination transfer of uterine prostaglandin E2 in early pregnant sow and its physiological consequences.

The local destination transfer of prostaglandin E2 (PGE2) from the uterine lymph to arterial blood supplying the ovary and its retrograde transfer to arterial blood supplying the uterine horn and the effect of additional delivery of PGE2 into the ovary on the secretion of steroid hormones was studied in early pregnant gilts. The injection of PGE2 under the perimetrium caused an increase (P<0.001) in PGE2 concentration in both uterine venous effluent and ovarian and uterine arterial blood. The infusion of PGE2 into the ovarian artery increased the concentration of progesterone in ovarian venous blood on day 13 of pregnancy during (P<0.05) and after (P<0.001) infusion, and on day 14 of pregnancy after infusion (P<0.01). In conclusion, local destination transfer of PGE2 from uterine lymph and venous blood to the ovary may affect luteal function, and retrograde transfer of PGE2 to the arterial blood supplying the uterus may contribute to the prevention of regressive changes of the endometrium in early pregnant gilts.

Mechanisms ensuring optimal conditions of implantation and embryo development in the pig.

The paper summarizes results of a series of studies concerning luteolysis and early pregnancy in pigs. The involvement of the oxytocin (OT)/OT receptor system in the mechanism of corpus luteum (CL) protection during early pregnancy as well as the implication of luteinizing hormone (LH) in the endometrial prostaglandin (PG) release and synthesis are described. In addition, the role of leptin in the regulation of ovarian steroidogenesis and the expression of leptin and its receptor (OB-Rb) genes in hypothalamus, pituitary and reproductive tissues are reported. Moreover, a strong emphasis was placed on the mechanism of PGE2 participation in the local endocrine regulations of reproductive processes occurring in the utero-ovarian area as well as on the vascular endothelial growth factor (VEGF) ligand-receptor system in the ovary and uterus.

Local transfer of prostaglandin E2 into the ovary and its retrograde transfer into the uterus in early pregnant sows.

This study was designed to establish (a) whether prostaglandin E2 (PGE2) can reach the ovary and oviduct by a local pathway and what is the contribution of lymphatic vessels to this transfer, and (b) whether PGE2 can permeate from venous and lymphatic vessels of the mesometrium to arterial blood and be delivered to the uterine horn during maternal recognition of pregnancy in gilts. The reproductive tract was excised from gilts (n = 10) on day 14 after mating. The uterine horn was isolated with the ovary and broad ligament and perfused with warmed and oxygenated autologous blood. A total dose of 5.5 x 10(7) disintegrations per min (d.p.m.) (49 ng) [3H]PGE2 was infused into the small branches of the uterine vein on the broad ligament or into the lymphatic vessels. Frequent blood samples were collected from the branch of the uterine artery and from the venous effluent. Tissue samples were collected from the uterine horn, the ovary and the broad ligament. The concentration of [3H]PGE2 was significantly higher in the ovary (P < 0.001), oviduct (P < 0.01), endometrium (P < 0.01), myometrium (P < 0.001) and mesometrium (P < 0.001) after infusion of [3H]PGE2 into lymphatic vessels than into the branches of the uterine vein. In contrast, the concentration of [3H]PGE2 was significantly higher in arterial blood supplying the uterine horn (P < 0.01) and in the venous effluent (P < 0.001) after infusion of [3H]PGE2 into the branches of the uterine vein than into lymphatic vessels. These results demonstrated local transfer of [3H]PGE2 into the ovary, oviduct and uterine horn from lymphatic and venous vessels of the mesometrium. However, the efficiency of this transfer was considerably higher after infusion into lymphatic vessels than into branches of the ovarian vein. We conclude that the lymphatic pathway is a fundamental mechanism in the local transfer of PGE2 from the uterus to the ovary and oviduct during early pregnancy in the pig.

The oestrous cycle and early pregnancy--a new concept of local endocrine regulation.

Facts discovered in recent decades have compelled us to revise long-established views on the physiological regulation of cyclic adjustments to the reproductive system in preparation for pregnancy in females. Evidence has been presented to show that changes in the uterine blood supply induced by the oestrogen/progesterone ratio in the blood and cytokines are important in the regulation of the secretory function of the endometrium. Progressive reduction in uterine blood flow during the luteal phase of the oestrous cycle causes regressive changes in endometrial cells and release of prostaglandin (PG) F(2 alpha), resulting in initiation of luteolysis. Retrograde transfer of PGF(2 alpha) in the area of the mesometrium vasculature is an important element in the mechanism protecting the corpora lutea against luteolysis before day 12 of the porcine oestrous cycle and during early pregnancy and pseudopregnancy. Results of many studies presented in this review indicate that PGF(2 alpha) pulses in uterine venous blood during the follicular phase of the oestrous cycle may not be due to PGF(2 alpha) secretion by endometrial cells, but occur due to remodeling of the endometrium and pulsatile exretion of PGF(2 alpha) in accordance with rhythmic uterine contractions caused by oxytocin.

Intramuscular injections of male pheromone 5 alpha-androstenol change the secretory ovarian function in gilts during sexual maturation.

In addition to the standard olfactory pathway typical for signaling pheromones, the existence of a humoral pathway for the priming action of pheromones has been earlier postulated. In this study in vivo experiment was performed to establish whether intramuscular injections of boar pheromone, 5 alpha-androstenol (5 alpha-androst-16-en-3-ol), might change the development and secretory function of the ovarian follicles during sexual maturation of gilts. Gilts from groups I (n=15) and II (n=13) received androstenol (10 microg/gilt/injection; i.m.) three times a week from day 192 to 234 of age. Similar, control gilts (group C; n=13) received saline. Additionally, the nasal cavity of animals from group II was irrigated with zinc sulfate solution to depress olfactory function. The reproductive organs and follicular fluid were collected on day 240 of age. There were no significant differences among groups concerning the weight of the ovary and uterus, the length of the uterine horns and intensity of cytochrome P450(scc) and P450(arom) immunoexpression. However, gilts treated with boar pheromone had a higher (p<0.01) total number of follicles > 3 mm in diameter and a lower index of atresia. In addition, androstenol-treated animals were characterized by higher concentrations of progesterone (the 1-3 mm and 3-6 mm follicles; p<0.01 and 0.001, respectively) and estradiol (follicles 3-6 mm; p<0.001) than those of controls. The results of the present study demonstrate that intramuscular injections of androstenol stimulate the development and secretory function of the ovarian follicles in gilts during sexual maturation. They also support the hypothesis that androstenol, as a priming boar pheromone, may influence reproductive processes in female pigs acting as a chemical signal via humoral pathway.

Uterine blood supply as a main factor involved in the regulation of the estrous cycle--a new theory.

The paper presents a new theory on the physiological mechanism of initiation of luteolysis, function of endometrial cells and protection of corpus luteum. This theory is based on previous studies published by the authors and their coworkers on the retrograde transfer of PGF2alpha in the uterine broad ligament vasculature during the estrous cycle, early pregnancy and pseudopregnancy. The studies were focused on cyclic changes in uterine blood supply and the apoptosis of endometrial cells. Moreover, the results of many other authors are cited. The statements of the theory are as follows: 1. The initiation of luteolysis is a consequence of regressive changes in the endometrium which are due to the reduction of the uterine blood supply below the level necessary to provide for the extended needs of active endometrium. 2. During the luteal phase, both a considerable increase in uterine weight and a decrease in blood flow through the uterine artery, resulting from increasing progesterone concentration, reduce the uterine blood supply. In comparison to the volume of blood flowing to the porcine uterus during the estrus period, only 30-40% of the blood volume is determined on day 12 of the estrous cycle. The uterine weight at that time is 40-60% larger than that in the early luteal phase. Thus, due to the considerable constriction of uterine blood vessels, there is a discrepancy between the requirement for oxygen and other factors transported by blood and the possibility of supplying the uterus with these substances. After reaching the threshold of uterine blood supply level, which in pigs takes place around day 12 of the estrous cycle, regressive changes and PGF2alpha release from endometrial cells occurs. 3. Estrogens and progesterone are the major factors affecting blood flow in vessels supplying the uterus. The factors that modulate, complement and support vasodilation and vasoconstriction are: PGE2, LH, oxytocin, cytokines, neurotransmitters and other local blood flow regulators. In some animal species these modulators, especially those of embryonic origin, may be crucial for the status of uterine vasculature. 4. During early pregnancy, the action of embryo signals (estrogens, cytokines), endometrial PGE2 as well as LH results in the relaxation of the uterine artery (pigs: day 12) and, consequently, in an increase in uterine blood supply. This reaction of the maternal recognition of pregnancy effectively prevents regressive changes in well developed endometrial cells to occur. 5. Local uptake and retrograde transfer of PGF2alpha into the uterine lumen during early pregnancy protects corpus luteum from PGF2alpha luteolytic action. 6. During the period of regressive changes resulting from the limited uterine blood supply, endometrial cells restrain PGF2alpha synthesis. They are, however, still capable of releasing prostaglandin when uterine blood supply is improved after the embryo appears in the uterus. This potential capability for PGF2alpha synthesis was demonstrated in in vitro studies when endometrial cells collected during its regressive phase were incubated in medium and stimulated by LH and oxytocin. 7. Prostaglandin F2alpha pulses in venous blood flowing from the uterus do not confirm pulsatile secretion of PGF2alpha. The pulses may result from the pulsatile excretion of PGF2alpha with venous blood according to the rhythmic uterine contractions associated with oxytocin secretion. 8. The results supporting this concept are presented and discussed in due course. The critique of Bazer and Thatcher's theory on exocrine versus endocrine secretion of prostaglandin F2alpha during the estrous cycle is also depicted.

Local adjustment of blood and lymph circulation in the hormonal regulation of reproduction in female pigs--facts, conclusions and suggestions for future research.

Arteries, veins, capillaries and lymphatic vessels situated in the mesovarium and mesosalpinx of domestic animal species (pig, cow, sheep) form the periovarian vascular complex. Particular components of the periovarian vascular complex interact functionally and morphologically creating a specific environment for numerous physiological processes. The complex plays an essential role in the system of the retrograde transfer of the ovarian hormones. This phenomenon is especially well documented in pigs. The efficiency of the retrograde transfer of estradiol and progesterone from blood and lymph leaving the gonad to blood of the ovarian artery (expressed as percentage of their concentration in the ovarian venous blood) as well as the rate of the retrograde transfer of these hormones to the ovary (measured in nanograms or picograms per minute) is presented and discussed in this paper. No simple relationship was found between hormone concentration in ovarian venous effluent and the efficiency or the rate of their retrograde transfer during the estrous cycle. It appears that two processes contribute to the highly efficient retrograde transfer of ovarian hormones into the ovary in the periovarian vascular complex: 1/ direct hormone permeation from the ovarian vein into the adjacent branches of the ovarian artery through the counter-current mechanism; 2/ indirect permeation of ovarian hormones consisting of two stages. The first stage includes the permeation of hormones from lymph leaving the ovary via the subovarian lymphatic vascular network as well as lymph and venous blood, leaving the mesosalpinx and going to capillaries and tiny venous vessels in the entire mesovarium. These tiny mesovarium vessels connect and then branch out again to form the veno-venous network on the surface of branches of the ovarian artery. The second stage includes the permeation of hormones from the veno-venous blood into the branches of the ovarian artery. The authors present a hypothesis that the retrograde transfer of ovarian hormones may participate in the feedback regulation of ovarian function. The relationship between the retrograde transfer of ovarian hormones in the area of periovarian vascular complex and local elevation of steroid hormone concentrations in blood supplying the oviduct and uterus is presented. The paper also includes suggestions for future research.