The neurohypophyseal capillary bed. I. Anatomy and arterial supply.

Vascular casts of the pituitary-median eminence complex of mice,rats, dogs, sheep and monkeys were examined with the scanning electron microscope. Microfil-injected specimens of the rabbit and monkey pituitary-median eminence complex were examined by light microscopy after intracranial internal carotid artery occlusion. In each species a common neuropophyseal capillary network was found uniting infundibulum (median eminence), infundibular stem and infundibular process. This capillary bed is supplied from above by superior hypophyseal arteries and from below by inferior hypophyseal arteries. An artery to the infundibular stem was found in some species. With occlusion of the intracranial internal carotid arteries, flow through superior hypophyseal arteries did not occur. Yet the entire neurohypophyseal capillary bed filled upon injection with Microfil. These observations suggest the concept of a restricted arterial supply to the median eminence with drainage to the underlying adenohypophsis on one hand and to the infundibular process with drainage to the systemic circulation on the other must be modifed and that blood flow within the neurohypophyseal capillary bed (between infundibular process and median eminence) occurs.