Hypophyseal angioarchitecture of common tree shrew (Tupaia glis) revealed by scanning electron microscopy study of vascular corrosion casts

Abstract

The vascular corrosion cast technique in conjunction with scanning electron microscopy (SEM) was used for the study of pituitary microvascularization in the common tree shrew (Tupaia glis). The pituitary vascular casts were obtained by infusion of low viscosity methyl methacrylate plastic (Batson's no.17) mixture. It was found that the blood supplies to the pituitary complex were from branches of the circle of Willis and could be divided into two groups. The first group consisted of two to four superior hypophyseal arteries (SHAs) branching off from the internal carotid artery supplying each half of the median eminence (ME), infundibular stalk (IS), and pars distalis (PD). The SHAs supplying the ME branched into internal and external capillary plexi. The internal plexus had a larger capillary size (approximately 15 microns in diameter), was deeper in position, and had denser and more complex capillary loops than those in the external plexus. The capillaries of the external plexus were approximately 10 microns in diameter. The two plexi drained into 15-20 hypophyseal portal veins (HPVs) which were located mainly along the ventral and ventrolateral surfaces of the IS before breaking up into large capillaries (approximately 18 microns in diameter) with an anteroposterior arrangement within the PD. The second group consisted of one inferior hypophyseal artery (IHA) on each side branching off from the internal carotid artery. These arteries gave off branches to pierce the dorsolateral and ventrolateral aspects of infundibular process (IP) before branching off to form a capillary network. They also gave rise to radiating capillaries to supply the pars intermedia (PI) surrounding the cortical area of the IP. The hypophyseal cleft separating the PI from the PD was clearly seen with very few blood vessels. The capillaries in both PD and IP joined to form confluent hypophyseal veins draining the blood into the cavernous sinus.

Types of vascular wall as related to vasa vasorum in common tree shrew (Tupaia glis)

“…This method is very useful to study the blood supply of various organs such as the exocrine glands (Haratake et al, 1990;Pradidarcheep et al, 2000), endocrine glands (Sudwan et al, 1991;Thongpila et al, 1998), nervous tissues (Chunhabundit et al, 1993a;Poonkhum et al, 2000), experimental angiogenesis of arterial vasa vasorum (Bayer et al, 2002), and others. This technique was applied in the present study to differentiate the types of blood supply to the vascular walls.…”

Testicular microvascularization in the common tree shrew (Tupaia glis) as revealed by vascular corrosion cast/SEM and by TEM

“…This finding is quite unique since the capillaries in other endocrine glands of the same animals including pineal , thyroid , pituitary (Sudwan et al, 1991), endocrine pancreas (Bamroongwong et al, 1992), and adrenal (Thongpila et al, 1997) are with fenestrations. The presence of continuous capillaries in this endocrine gland leads to the speculation that the androgens produced by the Leydig cells may pass directly through the capillary wall since the steroid hormones could easily propagate through the cell membrane (Daryl, 1993).…”

Untitled

“…With this technique, the vascular patterns in the pituitary-median eminence complex have been studied in the rabbit 17 and rat 8,9 . This technique has also elucidated the vascular pattern in pituitary gland of common tree shrew (Tupaia glis) 18 , the animal regarded as a primitive primate. 19,20 As detail hypothalamic angioarchitecture of the tree shrew has not been studied, it is of interest to employ the vascular corrosion cast technique/SEM to elucidate this matter.…”