Urogenital vasculature and local steroid concentrations in the uterine branch of the ovarian vein of the female tammar wallaby (Macropus eugenii)

The urogenital vasculature of the tammar comprises 4 major paired arteries and veins: the ovarian, the cranial urogenital, the caudal urogenital and the internal pudendal artery and vein. The ovarian artery and vein and their uterine branches which supply the ovary, oviduct and uterus, ramify extensively. Each anterior urogenital artery and vein supplies the caudal regions of the ipsilateral uterus, lateral and median vagina and cranial parts of the urogenital sinus. The caudal urogenital arteries and veins supply the urogenital sinus and caudal regions of the bladder. The internal pudendal artery and vein vascularize the cloacal region, with some anastomoses with branches of the external pudendal vessels. Anastomoses connect the uterine branch of the ovarian artery with the uterine branch of the cranial urogenital and cranial branches of the caudal urogenital arteries, and connect the caudal urogenital and the internal pudendal arteries. Anastomotic connections between the left and right arterial supply also occur across the midline of the cervical regions of the uteri and the anterior lateral vaginae. Similar connections are seen in the venous system. The uterine branch of the ovarian artery ramifies extensively very close to the ovary, giving a plexiform arrangement with the ovarian veins, and also with the uterine venous system on the lateral side of each uterus. This plexiform structure provides an anatomical arrangement which could allow a local transfer of ovarian hormones from ovarian vein into the uterine arterial supply, and thence to the ipsilateral uterus. Progesterone concentrations in plasma from the mesometrial side of the uterine branch of the ovarian vein are markedly higher than in tail vein plasma, especially during the 'Day 5 peak' early in pregnancy, and also at full term. There is also a marked decrease in progesterone concentration from all sites immediately before birth as previously reported for peripheral plasma. These results support the suggestion of a countercurrent transfer mechanism, at least for progesterone, and possibly other hormones, between the ovarian vein and uterine artery. Such a local transfer could explain the different morphological responses of the endometria of the two adjacent uteri during pregnancy in macropodid marsupial species.     

Local exchange of oxytocin from the ovarian vein to ovarian arteries in sheep

Local transfer of 125I-labeled oxytocin from the ovarian vein to arteries supplying the ovary, the oviduct, and the tip of the uterine born has been investigated. In five sheep, 10 infusions of 125I-oxytocin over a period of 1 h were performed, and the concentration of labeled polypeptide in the peripheral plasma was compared to ovarian arterial plasma. During 2 consecutive infusions into each animal's ovarian vein, blood was collected simultaneously from the following sites: ovarian branch of the ovarian artery (OBOA), tubal branch of the ovarian artery (TBOA), uterine branch of the ovarian artery (UBOA), and from the jugular vein. In all experiments the concentration of 125I-oxytocin in ovarian arterial plasma was higher than in peripheral plasma. The ratio of ovarian artery/jugular vein for 125I-oxytocin was: OBOA 2.8, TBOA 1.8, UBOA 1.6. Based on a 4 ml/min blood flow through ovarian arteries supplying ovary, oviduct, and the tip of the uterine horn, the local transfer of the total amount of oxytocin infused was estimated to be about 1% (range: 0.1-4.4%). Analysis of variance did not reveal significant differences in the exchange ratios between OBOA, TBOA, and OBOA. However, the variances within these groups are significant, presumably because of anatomical variation in the degree of surface contact area between arteries and veins at the ovarian pedicle. It is concluded that polypeptides are locally recirculated to ovaries, oviduct, and the tip of the uterine horn in a higher concentration than is supplied by peripheral blood. This could provide a mechanism for local distribution and concentration of the ovarian peptides that regulate reproductive 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.     

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.     

Progesterone in uterine and arterial tissue and in jugular and uterine venous plasma of sheep

Concentrations of progesterone in uterine and arterial tissue and in uterine and jugular venous plasma were determined. Blood was collected on Days 4 and 9 postestrus from the jugular vein and the first and last venous branches draining each uterine cornu; uterine tissue and arteries were subsequently collected. Progesterone was greater (p less than 0.05) in the cranial third than in the middle or caudal thirds of the uterine horn adjacent to the corpus luteum (CL)-bearing ovary or in any third of the contralateral horn. Progesterone in uterine arterial segments adjacent to the CL-bearing ovary was higher (p less than 0.05) than in contralateral segments. Progesterone was higher (p less than 0.05) in blood from the first venous branch of the cranial third of the uterine cornu adjacent to the ovary with the CL, than in the last branch of the caudal third, or contralateral horn, or in jugular blood. When oviductal veins were resected on Day 9 postestrus, progesterone in the first vein draining the cranial third of the uterine cornu adjacent to the CL-containing ovary was not different (p greater than 0.05) 48 h after resection than in the same vessel in the opposite horn or in jugular blood. We concluded that progesterone and other ovarian products may be delivered to the uterus locally.     

Distribution of progesterone to the uterus and associated vasculature of cattle

Multiparous dairy cows were sampled to study the concentrations of progesterone in tissue of the uterus and associated vasculature and to determine whether progesterone was delivered to the uterus locally. In study 1, progesterone was greater (p less than or equal to 0.05) in the first venous branch draining the cranial portion of the uterine cornu adjacent to the vary with a corpus luteum than in jugular blood or in the same vein draining the opposite uterine cornu on day 11 postestrus. Concentrations of progesterone were also greater (p less than or equal to 0.05) in the cranial than in the caudal half of the uterine cornu adjacent to the luteal-bearing ovary or in the cranial and caudal halves of the opposite uterine cornu. Concentrations of progesterone were also greater (p less than or equal to 0.05) in the uterine or ovarian arterial tissue adjacent to the ovary with the corpus luteum than in those same vessels on the contralateral side. In a second study, progesterone at 0 h on day 11 postestrus was greater (p less than or equal to 0.05) in the first venous branch draining the cranial portion of the uterine horn adjacent to the luteal-bearing ovary than in jugular blood, the same vein in the contralateral uterine cornu or in the same uterine vein 48 h after ligation and resection of the oviductal vein adjacent to the ovary with the corpus luteum. It is concluded that progesterone is delivered locally to the uterus and associated vasculature and the route of local delivery appears to be via the oviductal vein.     

Comparative analysis of functions of cow and reindeer female reproductive organs: Progesterone content in vessels of reproductive organs

Progesterone content in blood from paired ovarian and uterine veins as well as from jugular veins of cows and reindeers was studied in the estrous cycle lutein phase and at the earlier stages of pregancy. In the both species, maximal progesterone concentration was detected in blood from vein of the ovary carrying corpus luteum (p < 0.001). In cows, a higher hormone concentration, as compared with jugular vein, has also been determined in vein of the uterus horn closest to ovary with corpus luteum (p < 0.01). In reindeers, blood from all studied vessels of reproductive organs had the progesterone concentration that was statistically significantly higher (p < 0.001) than that from jugular vein. In cows, progesterone concentration in blood from the ovarian vein was found to be higher when corpus luteum was located on the right ovary (p < 0.05) as compared with left-side corpus luteum location. No functional asymmetry of ovaries was revealed in reindeers. A possible role of mechanisms of the hormone local transport between ovary and uterus in adaptation of ruminants to reproduction under Nordic conditions is discussed.     

Components of oviduct physiology in eutherian mammals

Recalling the evolutionary sequence of development first of gonad and subsequently of oviducts, ovarian endocrine regulation of all known components of oviduct physiology is reviewed. Ovaries not only influence oviducts via the systemic blood circulation, but also locally by counter‐current transfer of relatively high concentrations of steroid hormones and prostaglandins between the ovarian vein and oviduct branch of the ovarian artery. The efficiency and impact of such counter‐current transfer is greatest around the time of ovulation, the transfer process receiving further inputs from hormones present in peritoneal fluid. Classical oviduct physiology is summarised, and the potential molecular consequences of temperature gradients within the duct lumen examined. At ovulation, an oocyte‐cumulus complex is displaced in minutes from the follicular surface to the site of fertilisation at the ampullary‐isthmic junction of the oviduct. This rapid initial phase is contrasted with the subsequent slow progression of embryos to the uterus in days, still encompassed within a zona pellucida. Regarding transport of spermatozoa, the formation of a pre‐ovulatory reservoir in the caudal portion of the oviduct isthmus is noted, with suppression of motility and sperm‐head binding to epithelial organelles acting to maintain fertilising ability. Completion of capacitation is prompted shortly before ovulation, predominantly by Ca²⁺ influx into bound spermatozoa. A controlled release of spermatozoa coupled with their hyperactivation results in initial sperm:egg ratios at the site of fertilisation close to unity, thereby avoiding the pathological condition of polyspermy. Both the oviduct milieu and embryonic development are influenced by paracrine activity of follicular granulosa cells released at ovulation and remaining in suspension in the vicinity of the oocyte or embryo. These cells may amplify early pregnancy signals from a zygote to the endosalpinx. Beneficial effects of the oviduct on domestic animal embryos are contrasted with anomalies arising as a consequence of in vitro culture. Primate embryos do not require exposure to an oviduct for normal development, perhaps due to overlapping compositions of endosalpingeal and endometrial secretions. Additionally, primate endometrial secretions may be modified by viable gametes or an embryo in the presence of a cumulus cell suspension.     

Dihydrotestosterone secretion in pregnant and pseudopregnant rats

The objective of this study was to determine levels of dihydrotestosterone in the peripheral circulation and the source of its secretion throughout pregnancy and pseudopregnancy. Rats were bled from the jugular vein and ovarian or uterine vein from Day 8 through Day 22 of pregnancy and from Day 8 through the end of pseudopregnancy in various types of pseudopregnant rats. Jugular vein samples alone were obtained on the day of parturition and every fourth day thereafter during the lactational period. Our results indicate that the levels of dihydrotestosterone in the peripheral circulation were high throughout pregnancy and pseudopregnancy then declined during the lactational period. The sources of dihydrotestosterone were primarily the ovary in pseudopregnant rats and the ovary plus uterus in pregnant rats.     

Ovarian and uterine lymphatic drainage in Australian flying-foxes (genus Pteropus,suborder Megachiroptera)

Ovarian lymphatics of flying-foxes were traced to determine if they could transport hormones directly from ovary to ipsilateral uterine horn, thereby stimulating the localised endometrial growth which is characteristic of these animals. Intra-ovarian injections of ink and serial histological sections did not reveal any such connection. All major ovarian lymphatics and those from the cranial tip of each uterine horn drain cranially, terminating in 1 or 2 lymph nodes lying caudal to the ipsilateral kidney. For much of their course, the major ovarian lymphatics run in the adventitia of the ovarian venous sinus. This sinus encloses the coiled ovarian artery, which provides the major blood supply to the cranial end of the ipsilateral uterine horn. Some fine ovarian lymphatics run in the adventitia of the coiled ovarian artery. The enclosure of the coiled ovarian artery by the ovarian venous drainage is thought to provide the main route for transfer of steroids from ovarian vein to ovarian artery and thence to ipsilateral uterine horn. The ovarian lymphatics described here do not bypass the vascular pathway but provide an additional route for counter-or cross-current transfer of ovarian steroids to the ovarian arterial supply to the uterus.     

Flow and composition of lymph from the ovary and uterus of cows during pregnancy

Ovarian or uterine lymph was collected continuously for periods of up to 25 days from 16 cows cannulated at stages of pregnancy ranging from 96 to 278 days post coitum. Blood samples were taken acutely from the ovarian and uterine veins during surgery and periodically from the jugular vein during the course of lymph collection. The flow rate and cell content of lymph was measured and blood and lymph plasma samples were analysed for progesterone, pregnenolone, pregnenolone sulphate, androstenedione, testosterone, oestrone, oestrone sulphate, oestradiol-17 beta, prostaglandin (PG) F-2 alpha, total protein and albumin. There was a high flow rate of protein-rich lymph from luteal ovaries with rates up to 101.7 ml/h occurring in individual lymphatics over short periods. Peripheral ovarian and uterine lymph contained a low concentration of cells (mean less than 10(5) cells/ml) comprising about 82-87% lymphocytes, 11-14% macrophages and monocytes and 2-4% other cells. At all stages of pregnancy, the concentration of progestagens and androgens was higher in ovarian lymph than in uterine lymph or blood plasma. The differences were greatest for progesterone and androstenedione which occurred at 200-fold and 60-fold greater concentration respectively in ovarian lymph than in jugular plasma. When serial 10 min samples were collected over a 12-h period, the concentration and output of progesterone in ovarian lymph varied in a phasic manner, ranging from 3.5 to 7.6 microM and from 31.7 to 293.1 nmol/h respectively. There was a positive correlation between the output of progesterone in lymph and the progesterone concentration in jugular blood samples taken every 20 min. During most of pregnancy there was little difference between the concentration of oestrogens in ovarian lymph, ovarian venous plasma and jugular plasma but, during the 3-5 days before calving, these hormones occurred at slightly higher concentration in ovarian lymph. Apart from pregnenolone and androstenedione, all steroids occurred at lower concentrations in uterine lymph than in jugular plasma. Shortly before parturition there was an abrupt increase in the concentration of PGF-2 alpha in uterine lymph. Lymph reflects more accurately the milieu of tissue cells than efferent blood and further analysis of differences in the concentration of substances in lymph relative to the output in the ovarian and uterine arterial and venous blood may lead to the identification of factors important in local regulatory mechanisms in the reproductive tract.     

Role of mesovarium and mesosalpinx in counter current exchange of hormones

On the base of own studies with counter current transfer of steroid hormones and PGF2 alpha and the data taken from the literature it is suggested that two parts of broad ligament of the uterus i.e. mesovarium and mesosalpinx are not only morphological structures keeping the ovary, oviduct and ovarian vasculature, but that they may take part in hormonal regulation of the ovarian function.     

Direct venous-arterial transfer of 125I-radiolabelled relaxin and tyrosine in the ovarian pedicle in sheep

125I-labelled relaxin and tyrosine were infused into the ovarian vein to investigate transfer to branches of the ovarian artery at the ovarian pedicle in sheep. The ovarian arteries supply the ovary, the oviduct, and the tip of the uterine horn. An exchange of relaxin (n = 24) and tyrosine (n = 18) was observed in blood samples collected from all branches of ovarian arteries. This is expressed as a ratio of radioactivity greater than 1 between jugular venous blood plasma and arterial blood plasma. The average ratio (+/- s.d.) over the total infusion period of 1 h was 1.42 (+/- 0.35) for relaxin and 1.69 (+/- 0.38) for tyrosine with maximal values up to 4.9 and 2.9, respectively. Of the total amount of substance infused (348 pmol/h), 0.22% of the relaxin and 1.19% of the tyrosine reached the adjacent arteries directly. From these investigations it is concluded that molecules with a molecular weight of approximately 6000 can be transferred directly from veins to arteries at the ovarian pedicle, and the efficiency of this exchange does not only depend on molecular size.     

NPY: its occurrence and relevance in the female reproductive system

Neuropeptide Y (NPY), an amidated peptide composed of 36 amino acid residues, is the most widely distributed neuropeptide that performs a broad spectrum of physiological functions in both the central and peripheral nervous systems. Among numerous other actions, this peptide is involved, at the periphery, in the neural regulation of blood pressure and blood flow through the organs, and also, acting via Y2 and/or Y5 receptors, in the regulation of angiogenesis. NPY influences blood vessels via its own Y receptors, predominantly of the Y1 subtype. As a sympathetic co-transmitter NPY causes vasoconstriction, stimulates vascular growth and potentiates the contractile activity of noradrenaline (NA), and as a parasympathetic neurotransmitter it is involved in the regulation of vasodilatation within e.g. the uterine artery. In the female reproductive system, NPY not only regulates the blood flow, but also the contractile activity of non-vascular smooth muscle cells of the uterus and oviduct, as well as the secretory function of the ovary. Both the concentration of NPY and its influence on the blood flow through the female reproductive organs are finely tuned by fluctuations in the concentration of ovarian steroid hormones. Thus, the present review was aimed at summarizing the current knowledge dealing with the physiological relevance of NPY in the regulation of female gonad and genital tract function, with a special regard to the pig as a model animal.     

Arterial component of the angioarchitecture of the canine ovary

In order to study and possibly identify a vascular pattern in the canine ovary, 30 ovarian specimens received arterial injections of a mixture of 'Micropaque' with hydrosoluble red pigment, followed by clearing. The aorta or the femoral artery was catheterized and the injection was performed under a constant pressure of 120 mm Hg. The blood supply of the ovary is provided by the ovarian and the uterine artery. The former appears to be the most important of the two arteries since it is the largest and is the origin of a very rich vascular net in the ovarian stroma. It follows a helicine course within the broad ligament and enters into the ovarian stroma either by a single trunk or by two divergent branches, each supplying the anterior and the posterior half. When there is only a single trunk, one can see a vascular tuft totally occupying the stroma, with tortuosities running in the same direction as the longitudinal axis of the ovary. When there are two branches, the distribution is similar but with two tufts instead of one. From the ovarian artery several branches arise, the largest and most frequent being the lateral tubal artery and a branch which anastomoses with the uterine artery in the mesovarium. Other branches anastomose with one another or with branches of the uterine artery, forming a rich vascular net along the mesovarium. The uterine artery is situated within the broad ligament and runs along the lateral border of the uterus and up to the superior extremity of the uterus where it ends.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of ovarian hormones on the rat oviductal and uterine concentration of noradrenaline and 5-hydroxytryptamine

This paper describes the effects of estradiol and progesterone on the concenirations of noradrenaline and 5-hydroxytryptamine in the Wistar rat oviduct and uterus. The levels of noradrenaline and 5-hydroxytryptamine are higher in the oviduct than in the uterus whereas p-tyrosine and tryptophan are similar in both tissues. Estradiol treatment reduced the oviductal concentration of noradrenaline but not 5-hydroxytryptamine in oviduct, while the concentrations of both noradrenaline and 5-hydroxytryptamine were reduced in uterine horn. The levels of noradrenaline in the oviduct and uterus in rats in estrus were lower than those of diestrous rats. Bilateral ovariectomy produced an increase in uterine noradrenaline and 5-hydroxytryptamine levels. These changes were reversed in the presence of ovarian hormones as indicated by experiments where unilateral ovariectomy was performed. Reserpine administration reduced noradrenaline concentration in both the oviduct and the uterus but did not change oviductal or uterine 5-hydroxytryptamine.These results indicate the existence of noradrenaline within postganglionic sympathetic nerve terminals and suggest that estrogens increase the utilization and the synthesis of noradrenaline in both the oviducts and the uterine horns. With respect to 5-hydroxytryptamine the data support the concept that it is mainly associated with mast cells.     

Relationship between cellular DNA synthesis,PCNA expression and sex steroid hormone receptor status in the developing mouse ovary,uterus and oviduct

The proliferative activities of the different cellular compartments of the developing mouse ovary, uterus, and oviduct were studied by radioautographic assessment of DNA synthesis with [³H]-thymidine labeling and by immunohistochemical staining of proliferating cell nuclear antigen (PCNA). The distributions of estrogen and progesterone receptors (ER and PR) were studied by immunohistochemical staining. The values of the PCNA positive staining indices were a little higher than that of the radioautographic labeling indices. However, linear relations were shown for the two indices. The proliferative activities were high from postnatal day 1–7 and decreased from day 14 in the different cellular compartments of the ovary. The proliferative activities were high on days 1, 3 and decreased from day 7 in the uterus and oviduct. Staining of ER and PR was very weak in the surface epithelium, stroma and large follicles of the ovary. Positive staining for ER occurred from day 14 in the uterine epithelium and from day 7 in oviductal epithelium. Positive staining for PR was observed from day 1 in both the uterine and oviductal epithelium. However, the positivity of both ER and PR occurred from postnatal day 1 in the stromal cells of the uterus and oviduct. These results suggest that the appearance of the steroid receptors differ between the different cellular compartment of the reproductive organs. The proliferative activities have an inverse relation with the expression of the steroid hormone receptors in the female reproductive organs during developmental stages. Therefore, we propose that there is an autonomous proliferation mechanism in the development of the reproductive organs or that the proliferation is moderated by factors other than steroid hormones.     

Effects of atrial natriuretic factor on maternal ovine vascular resistance

Atrial natriuretic factor (ANF) is a potent endogenous vaso-dilator and diuretic peptide of uncertain physiologic relevance. In this study, the effects of ANF on normal and angiotensin II constricted placental, uterine and renal vessels were examined in pregnant sheep. Ewes were equipped with catheters to monitor vascular pressures, infuse drugs and measure blood flow by the microsphere technique. An electromagnetic flow sensor was placed around the middle uterine artery and electromyogram electrodes were attached to the uterus. ANF was administered into a branch of the uterine artery to minimize its systemic effects. The experiment included two protocols. First, blood flows and pressures were measured after a 5-min period of saline infusion into the uterine artery. These measurements were repeated at the end of a 5-min infusion of ANF (6.25 micrograms.min-1) into the uterine artery. During the second protocol, angiotensin II (AII) was infused via the jugular vein at 5 micrograms.min-1 for 10 min and ANF (6.25 micrograms.min-1) was infused through the uterine artery during the second half of the AII infusion. In the absence of AII, ANF lowered blood pressure from 97 +/- 6 to 90 +/- 6 mmHg (P less than 0.05); and placental resistance from 67.8 +/- 11.3 to 57.3 +/- 10.4 mmHg.min.ml-1 per g (P less than 0.01). Uterine resistance did not change.(ABSTRACT TRUNCATED AT 250 WORDS)     

Counter current transfer in the female adnex

The utero-ovarian veins and lymph vessels are intimately connected with the ovarian artery in the human female and in domestic animals, with the exception of the horse and the human female. A direct, local exchange of molecules from veins and lymph vessels to arteries (counter current transfer) has been documented for this anatomic structure. Countercurrent transfer of certain inert gases (133xenon, 85krypton), of prostaglandins (PGF2 alpha), of steroid hormones (e.g. progesterone, estradiol, testosterone), and of small peptide hormones (oxytocin, relaxin) has been shown to occur in laboratory and domestic animals as well as in the human female. The transfer of the inert gases takes place within seconds. The transfer of steroid hormones and peptides is detectable within minutes while the transfer of PGF2 alpha is delayed for 20 minutes. Red blood cells or albumin are not transferred. The existence of the local transfer is postulated to be of importance for: 1) the pregnancy/non-pregnancy signal from the uterus and tube to the ovary. The signal may be a combination of a luteotrophic signal from the embryo and lack of a "non-pregnant" luteolytic signal from the endometrium, the latter probably being PGF2 alpha in some species; 2) the unilateral influence of the ovarian hormones on the function of the ovarian, tubal, and possibly uterine tissues. An active corpus luteum may create in a mono-ovulatory animal a higher progesterone level in arterial blood supplying the ipsilateral tube and ovarian interstitial tissue than on equivalent contralateral organs.