HORMONES AND THE CONTROL OF PORPHYRIN BIOSYNTHESIS AND STRUCTURE IN THE HAMSTER HARDERIAN-GLAND

The hamster Harderian gland seems to present both an excellent model f or the control of porphyrin biosynthesis and an unusually robust examp le of the interrelationship between structure and function. It has bee n known for some time that 1) the capacity for manufacturing and stori ng porphyrins and 2) gland histology and ultrastructure are controlled by androgens. Thus, in intact males as well as in gonadectomised anim als of either sex treated with androgens, porphyrin synthesis by the H arderian gland is suppressed and the gland tubules characteristically possess two cell types, the cytoplasm of both containing polytubular c omplexes. By contrast, the Harderian glands of intact females and cast rated males synthesise and store large amounts of protoporphyrin, whil e their tubules possess only one cell type which lacks polytubular com plexes. So overarching is the effect of androgens that they have been described as a ''coarse tuning'' effect on the gland. By contrast, the role of the ovary is both less dramatic and less well understood. In female hamsters, ovariectomy leads to degenerative changes in Harderia n gland tubules and (probably) a release of stored porphyrin; at the s ame time there is a reduction in enzyme levels and new synthesis. The causative hormone in this ''fine tuning'' is unclear at present. There is now clear evidence that the Harderian gland is also controlled dir ectly by pituitary hormones. In particular, the use of continuous infu sion osmotic minipumps has allowed us to demonstrate not only 1) that the expected rise in porphyrins and feminisation of gland morphology d oes not occur in castrated males receiving the dopamine agonist bromoc riptine, but that 2) the simultaneous administration of prolactin does permit these changes; furthermore, 3) the administration of prolactin alone increases porphyrin synthesis above the levels found in untreat ed castrates. Similarly, bromocriptine administration to ovariectomise d females markedly reduces porphyrin synthesis and masculinises gland structure; again, this is reversed by the simultaneous administration of prolactin. Prolactin must therefore be seen as equipotent with andr ogens in determining gland structure and activity. (C) 1996 Wiley-Liss , Inc.