Blood vascular bed of the rat pituitary intermediate lobe, with special reference to its development and portal drainage into the anterior lobe. A scanning electron microscope study of vascular casts.

Abstract

Summary. Blood vascular beds of the rat pituitary intermediate lobes were reproduced by injection of low viscosity methacrylate media, and then observed with a scanniag electron microscope. Although the intermediate lobes of newborn and pubescent rat were poorly vascularized, the adult rat intermediate lobe contained numerous capillaries forming a fairly independent network whose density, however, was not so great as in the anterior and posterior lobes. The vascular network of the intermediate lobe could be divided into two parts: a superficial plexus close to the anterior lobe, and a deep one close to the posterior lobe, though the two plexuses were continuous with each other. The superficial plexus consisted of anastomosing capillaries, and the deep one of non-anastomosing capillaries with a pallisadefashioned arrangement.The superficial plexus seemed crucially important for the blood supply of the intermediate lobe since it developed or thickened as the animals aged. The superficial plexus received its proper afferent vessels from the middle and posterior hypophyseal arteries and emitted its proper efferent vessels continuous with the sinusoidall capillaries of the anterior lobe. The capillaries of the deep plexus usually communicated with the arterial capillaries of the posterior lobe and possibly represented another afferent route to the superficial plexus. This paper, thus, strongly suggests a portal circulation from the intermediate lobe to the anterior lobe though its functional significance is unknown.

Blood vascular architecture of the rat cerebral hypophysis and hypothalamus. A dissection/scanning electron microscopy of vascular casts.

“…The present paper clearly shows that our low viscosity methacrylate media are useful for completely casting all the blood vascular beds of the hypophysis and hypothalamus (MURAKAMI, 1975a, b ;MURAKAMI et al, 1984MURAKAMI et al, , 1985. Our preliminary experiments in this study have shown that the commercially available Mercox media or Batson's plastic are so viscous that they are not always suited for complete infusion into such complicated capillary networks as those of the hypophysis and hypothalamus.…”

“…Some authors have claimed that the communications originate in the capillaries of the primary plexus, and thus regard them as a possible feed-back portal route from the hypophysis to the hypothalamus (BASIR, 1932;TOROK, 1960TOROK, , 1964BERGLAND and PAGE, 1979), others have maintained that they arise directry from the arterial branches in the primary plexus to supply the hypothalamic capillaries (DUVERNOY, 1972). Our previous studies by dissection/scanning electron microscopy of the methacrylate vascular casts of the monkey, dog and rat have supported the latter view of the arterial origin (MURAKAMI,1975a, b ;KIKUTA et al, 1984;MURAKAMI et al, 1985).…”

“…Scanning observation of the vascular casts has clearly comfirmed in the monkey, dog, rat and some other animals this, or long portal system, as well as the so-called short portal system connecting the infundibular process and pars distalis (MURAKAMI, 1975a, b ;PAGE et al, 1976PAGE et al, , 1978PAGE and BERGLAND, 1977;LAMETSCHWANDTNER et al, 1977;PAGE, 1978, 1979;OHTANI et al, 1983;KIKUTA et al, 1984;MURAKAMI et al,' 1985). Another short or intraadenohypophyseal portal system between the pars intermedia and pars distalis has been further documented in the rat (MURAKAMI, 1975a;MURAKAMI et al, 1985).…”

Intrapituitary Regulatory System of Proliferation of Mammotrophs in the Pituitary Gland

“…In mice, MC3-R mRNA is localized in most mammotrophs and some somatotrophs . Blood from the rat intermediate lobe to the anterior lobe flows through the portal link between the vascular network of the intermediate lobe and the sinusoidal capillaries of the anterior pituitary (Murakami et al, 1985). α-MSH released from the intermediate lobe can therefore reach mammotrophs in the anterior pituitary and stimulate PRL release and cell proliferation.…”

The Mammalian Pars Intermedia —Structure and Function—

“…Recently, a scanning electron microscope study of cast samples of the rat pituitary gland suggested that the capillary bed of the rat pars intermedia is a fairly independent unit, and a constant portal drainage system into the pars distalis (Murakami et al, 1985). The pars intermedia of the newborn rat pituitary gland is poorly vasculated.…”