Using light and electron microscopy, we have observed the presence of rays containing medullary tissue extending across the cortex of rat adrenal glands. Within these rays chromaffin cells, as well as collagen and nerve fibers, were present. It is suggested that these endocrine cells may have a paracrine function within the cortex, possibly via their secretory product.

The mitotic, trophic and secretory responses of the adrenal cortex to various preparations and doses of ACTH were investigated in the rat. 1-24-ACTH depot (Synacthen) elicited the highest mitotic and trophic stimulation. The mitotic stimulation occurred exclusively in the glomerulosa, the trophic stimulation occurred mainly in the fasciculata-reticularis and the functional stimulation was found in both, as indicated by the plasma aldosterone and corticosterone levels. The functional changes occurred first, the trophic changes later. Large doses of ACTH inhibited cell proliferation in the fasciculata. The trophic action consisted in an enlargement of the adrenal, to a great extent in the fasciculata-reticularis, and to a lesser extent in the glomerulosa. This enlargement was due partly to parenchymal cell hypertrophy, but also and mostly to stromal hypertrophy, especially hyperaemia. The largest dose of ACTH caused a considerable widening of the sinusoids of the fasciculata-reticularis and medulla, and possibly caused a loss of parenchymal cells in the reticularis. These effects are reminiscent of the well documented haemorrhagic conditions of the adrenals in humans.In a previous work dealing with the hyperplastic stimulation of the adrenal glomerulosa by various hormones, we had found little effect of ACTH on the glomerulosa (Payet 8c Isler 1976). When we later examined the zona fasciculata, which is the acknowledged target tissue of ACTH, paradoxical¬ ly we found no effect on this layer. Therefore, we decided to investigate this lack of effect in more detail, using various plain and long acting ACTH preparations and doses. Our findings are reported in this paper. They again are paradoxical since we found a considerable hyperplastic stimulation of the zona glomerulosa and a lack of such stimulation of the fasciculata. We also investigated the relation¬ ship between mitotic and secretory activity of the cortical layers. Materials and MethodsThe general procedure was the same as that described in a previous article (Payet & Isler 1976). Two months old female hooded rats were kept in individual cages, fed purina laboratory chow and water ad libitum, and han¬ dled daily during the week prior to the experiment to minimize the stress due to manipulation under treat¬ ment.Plain 1-39-ACTH was obtained from Schwartz-Mann Biochemical division of Picker Nuclear, Montreal, as a porcine preparation of 70 IU/mg potency; a similar preparation from Nordic Pharmaceuticals Ltd. was also used (Duracton); it is available in aqueous solution con¬ taining carboxymethyl-cellulose, dextrose and phenol.1-39-ACTH Depot was the Acthar Gel (H.P.) prepara¬ tion of the Armour Pharmaceutial Company and consists in a highly purified ACTH in an aqueous solution of 16% gelatin, 0.15% phenol and 0.1% cysteine.

Duct-like structures made of cells different from follicular or light cells were observed with the electron microscope in the thyroid glands of 16 rats. The wall of most of the ducts was made of two types of cells: (1) the lumen-bordering cells, mostly cuboidal or columnar, with short microvilli, and ( 2 ) the subjacent squamous cells, arranged in one or several layers of cells displaying numerous desmosomes and dense bundles of tonofilaments. Both cell types showed intricate folding of the plasma membrane at sites of cell-to-cell contact, an abundance of free ribosomes and nuclear indentations. In one occasion mucous-like cells were found. The lumen contained a finely granular homogeneous material as well as cell remnants. The ducts were located among the follicles, and were usually discrete from them; but on four occasions the epithelium of the duct was seen in direct continuity with that of a thyroid follicle. Only one case of a light cell associated with a duct was observed while many of these cells were associated with thyroid follicles.

Injection of posterior pituitary powder induces an intense mitotic stimulation in the zona glomerulosa of the adrenal gland of young rats. This effect is much more pronounced in females than in males. It is maximal at two days treatment. Longer periods result in a hypertrophied zona glomerulosa and lower mitotic activity. A search for the hormone responsible for the stimulation shows that vasopressin, and to a lesser extent oxytocin, are mitogenic. ACTH, alpha-MSH, beta-MSH and the pineal hormones have no effect. Renin (but not angiotensin) induces a significant stimulation. It is concluded that vasopressin exerts a potent influence on the glomerulosa. This is in contrast with the prevalent view that the glomerulosa is little affected by the hypophysis.