Injection of the reproductive tract vasculature with subsequent clearing (rendering transparent) of tissues allowed visualization and studying of the reproductive tract's vascular system in relation to the tissues it supplies. The technique was adopted from Orsini (1962) and Del Campo et al. (1974), with modifications as follows. Blood washout was performed with physiological saline at approximately the normal goat body temperature as a way to maintain the normal physiological state of vessels, including their diameter to facilitate injection, and to avoid extravasation of the injection medium. The use of an infusion pump instead of hand injection provides better control of intraarterial pressure, is documentable, and is reproducible. Microfil rather than latex was injected into the vasculature of the reproductive tracts. Microfil provides complete filling with minimal shrinkage of the vasculature, is easy to prepare, is available in many colors, does not require an acidic environment for curing, and is radio-opaque. Using equal quantity of Microfil and MV diluent resulted in a medium of very low viscosity with the ability to cross capillaries. Since capillary crossing was not desirable in this study, we used a mixture of MV and HV diluents to increase viscosity of the final product to avoid crossing of capillaries. We tried the clearing agents (benzol and benzyl benzoate) used by Orsini (1962) and Del Campo et al. (1974), but no satisfactory results were obtained. Methyl salicylate and glycerin were each used in our experiment as clearing agents, and both gave satisfactory results. Alcohol-methyl salicylate clearing produced a stiffer tissue, which, from an aesthetic point, provides a pleasing view for gross observation, but it is difficult to manipulate. Also, extended exposure to the strong smell of methyl salicylate was unavoidable (even under a fume hood) during the long study time required to examine such a complex vascular system as that of the reproductive tract. Glycerin clearing produced a more flexible tissue, allowing easier manipulation for a given area. Glycerin has a more pleasant smell than that of methyl salicylate, but from an aesthetic point, it does not provide such a pleasing view as that of methyl salicylate.
Because radiography was to be used to study the distribution of the reproductive tract vasculature, Microfil was chosen because of its radio-opacity. However, while radiographs were useful to study vessels' distribution, no more information was obtained from studying them than was available from studying cleared specimens examined with the naked eye. In other words, studying cleared specimens provided enough information to render radiographs unnecessary except perhaps to confirm visual impressions by a second visualization method. Further, due to the inherent disadvantage of radiographs in the form of superimposition of vessels in two-dimensional views, determining the definitive supply of certain area by certain branch was difficult.
The ovarian artery's tortuousity and close apposition to the uterine branch of the ovarian vein, seen in all specimens in this study, was discussed by Del Campo and Ginther (1973), though they did not examine goats. The higher effective dose of PGF2α in sheep is due to the presence of mainly a local utero-ovarian pathway in sheep versus a mainly systemic pathway in horses (Ginther,1974). Our study showed that goats are similar to sheep and therefore can be expected to have this local utero-ovarian pathway as well. Substances (such as PGF2α) can pass from the ovarian vein to the ovarian artery and affect the ovary.
Our work demonstrated that the architecture of the ovarian artery and vein was maintained throughout pregnancy. Maintenance of luteal function during early pregnancy in ewes (Mapletoft et al.,1976) and cows (Del Campo et al.,1980) occurs by local vascular transport of a luteotropic substance from the gravid uterus to the ipsilateral ovary. The nature and chemical properties of this substance were not investigated. The transport of luteotropic substance occurs by means of the close apposition of the ovarian artery to the ovarian vein. This physiological supposition is supported by the anatomic architecture of the utero-ovarian vasculature demonstrated in early pregnancy in ewe and cow, and by the anatomy revealed here for goats as well. Maternal recognition of pregnancy occurs around day 13–14 after ovulation in ewe and 15–16 in cows (Senger,2003). It is achieved by production of certain proteins between days 13 and 21 after ovulation. These include ovine trophoblastic protein 1 (homologous to interferon-α), or bovine trophoblastic protein 1, and pregnancy-specific protein B (pregnancy-associated glycoproteins; PAGs). Ovine and bovine trophoblastic proteins inhibit oxytocin receptor synthesis by endometrial cells and promote protein synthesis by endometrial glands. These proteins are not luteotropic. Pregnancy-specific protein B is produced by binucleate giant cells and has a luteotropic effect. Maternal recognition by means of production of trophoblastic protein 1 does not require a local venoarterial pathway between the uterus and ovary because it is produced in the uterus and acts on the uterus; however, the other protein (pregnancy-specific protein B) is produced in the uterus but acts on the CL so it does require a pathway to reach the ovary. Study by Bridges et al. (1999) proved that there was no luteal source of pregnancy-specific protein B in ewes. Pregnancy-specific protein can reach the ovary by either a local or a systemic pathway. We hypothesize that the predominant mechanism in ewes, cows, and does is the local one between the uterus and ovary. We base this hypothesis on the presence of the intimate arteriorenous approximation and its potential functionality as a local venoarterial pathway. More physiological studies are needed to test this hypothesis. Also, the molecular weight and possible mechanisms of transfer of PAGs should be considered in future studies. Pregnancy-specific protein B has a clinical importance. It can be used for pregnancy diagnosis in goats (Humblot et al.,1990).
Ewes are CL-dependent till 50 days of pregnancy; thereafter, the placenta produces sufficient amounts of progesterone to support pregnancy. Cows are CL-dependent till 6–8 months of gestation. Does are CL-dependent throughout the entire period of pregnancy (Senger,2003). Progesterone is produced almost entirely by the CL in goats, and ovarioectomy at any time causes abortion. The presence of this anatomic arrangement of utero-ovarian vessels has only been demonstrated in nonpregnant (Ginther,1976) and early stage pregnant ewes (Mapletoft et al.,1976) and cows (Del Campo et al.,1980). Whether this arrangement is present at later stages of pregnancy in ewes or cows has not been studied. This work shows that in the goat, this arrangement was in fact maintained throughout pregnancy, which fits the fact that the goat is CL-dependent throughout pregnancy. Factors produced by the placenta could be transported via this anatomic arrangement to maintain the CL throughout pregnancy. Whether CL maintenance is the only function of this anatomic arrangement cannot be elucidated without further studies on the presence of this anatomic arrangement of the ovarian artery and ovarian vein at later stages of pregnancy in ewes and cows, as well as further work coordinating the physiological and anatomic interrelationships in all ruminant species.
Special adaptations of the ovarian and/or vaginal arteries were noted in multiple pregnancies. First, in 66.7% of triplets, the size of the uterine branch of the right ovarian artery was about equal to that of the continuation of its parent artery. Second, in 16.7% of triplets, the size of the uterine branch of the left ovarian artery was actually larger than that of its parent artery. Third, in half of triplet pregnancies in the right side and 33.3% in the left side, the uterine branch of the ovarian artery gave off a branch that joined a branch of the uterine artery and supplied the uterine horn. Fourth, the uterine branch of the ovarian artery also gave off an additional branch that supplied the dorsal surface of the area adjacent to the tip of the uterine horn in half of the triplets. Fifth, in one doe with triplet pregnancies at 18 weeks of pregnancy, the left ovarian artery gave rise to an additional branch to the uterus; this branch was larger than the ipsilateral uterine artery. It supplied the entire dorsal surface of the left uterine horn and anastomosed with the uterine branch of the ovarian artery and uterine branch of the vaginal artery. Sixth, a connecting branch was present between the right uterine artery and the uterine branch of right vaginal artery in 16.7% of triplets. Seventh, a connecting branch was present between the left uterine artery and the uterine branch of left vaginal artery in 16.7% of triplets. These adaptations were observed in triplet pregnancies mainly at later stages. This physiological adaptation to multiple pregnancies has not been noted before in the literature. This may be due to lack of anatomical studies on uterine vessels during pregnancy in all animals. These adaptations presumably serve to provide an additional blood supply to the uterus in the case of multiple pregnancies due to the increasing demand of the growing fetuses.
No difference was observed in the origin and distribution of the ovarian, uterine, and vaginal arteries between pregnant and nonpregnant does; however, differences in these aspects existed within specimens from pregnant and/or non-pregnant does. The ovary is supplied by the ovarian artery. The infundibulum and the area of the uterine tube adjacent to the ovary are supplied by the uterine tube branch of the ovarian artery. The isthmus and area adjacent to the uterus are supplied by the uterine branch of the ovarian artery. The supply of the ampulla is mainly via the uterine tube branch, but in some cases via the uterine branch of the ovarian artery.
The uterus is supplied by branches of the ovarian arteries, uterine arteries, and vaginal arteries. The supply of different parts of the dorsal and ventral surfaces of the uterus is provided in Figure 12. This will be helpful to other researchers performing studies on the caprine reproductive organs. The dorsal and the ventral surfaces of the uterine tip and the adjacent area are supplied by the uterine branches of the ovarian arteries, which anastomose with branches of the uterine artery. The distribution of the caudal and cranial branches of the uterine artery was consistent in most of the specimens; however, in some specimens the cranial or caudal branch dominated to supply most of the dorsal or ventral surface, respectively, of the ipsilateral uterine horn. The dorsal and ventral surfaces of the area between the middle portion of the uterine horn to the tip were supplied mostly by the branches of the cranial branch of the uterine artery. The supply of the ventral surface of the middle area of the uterine horn was mainly by branches of the caudal branch of the uterine artery. The dorsal surface of the middle portion of the uterine horn was supplied about equally by either the cranial or caudal branch of the uterine artery. The ventral surface of the caudal part of the uterine horn was supplied by the caudal branch of the uterine artery in all specimens studied. The dorsal surface of the caudal part of the uterine horn was supplied by the caudal branch of the uterine artery in most specimens. The dorsal and ventral surfaces of the uterine body were supplied by both the caudal branches of the uterine arteries and uterine branches of the vaginal arteries.
The anastomosis between branches of the right and left uterine arteries introduces the possibility of mixing of substances between the two horns. Substances produced in or introduced into one horn can possibly move to the other horn, i.e., substances produced in a gravid horn may move to the nongravid horn or vice versa.
The uterine branch(es) of the right and/or left vaginal arteries anastomoses with branches of one or both caudal branches of the uterine arteries on the ventral surface and/or dorsal surfaces of the uterine body and caudal part of the uterine horn. The anastomosis was not ipsilateral in all cases; it was with the contralateral artery and/or both arteries (right and left) in some specimens. The size of the right and left vaginal arteries was not equal in some specimens; one or the other dominated to supply both the ventral and dorsal surfaces of the uterine body, while the other supplied just one surface.