In Vitro Models for Reading and Manipulating Trophoblast Signals

Abstract

Endocrine glands need information. They have to receive messages telling them how much of their hormones to produce and when to secrete them. For most endocrine glands the signalling system is well known, at least in outline. Thus gonadotrophin releasing hormone, a peptide of known constitution coming from the hypothalamus, informs the anterior lobe of the pituitary when and how much luteinising hormone to release. The whole system cannot operate unless there is a feedback from the site of action, telling the endocrine gland of the need for its hormone. The one exception appears to be the placenta. So far no feedback signals controlling the production of its many protein secretions, some of which are hormonal in nature, has been defined. A decade ago this curious circumstance led one endocrinologist to propound the despairing thesis that placental proteins have no biological function. There is no feedback signal from the site of action and the production rate of placental proteins is solely related to trophoblast mass and blood flow in the intervillous space.¹ Seven years later he saw no reason to modify his hypothesis.²