The aim of the study was to determine the effects of exogenous melatonin on Leydig cells in irradiation stress. Nuclear and cytoplasm surface of Leydig cells in sham pinealectomized and pinealectomized adult Wistar rats was determined after their total irradiation with 8 Gy of gama rays produced by 60 Co and with previously performed 14 days treatment by injecting of melatonin solution in a daily dose of 0.2 mg. Rats testes were histologically prepared 17 days after irradiation. Total melatonin administration significantly decreased surface of Leydig cells including both decrease of their nuclear and cytoplasm surface in irradiated sham pinealectomized and pinealectomized rats. The results suggested about direct effects of exogenous melatonin on Leydig cells in irradiation stress.

The effects of pinealectomy on the dynamics of morphometric changes in interdigitating cells(IDC) of rat thymus were investigated. The experimental animals were divided into two groups: an experimental one and the control group. Animals from the first group were subjected to pinealectomy while the second group were treated in the same manner, but without the removal of the pineal gland. All the animals were sacrificed 60. days following the surgery. The thymus tissue were fixed by means of immersion and prepared for transmission electron microscopy. Using Weibl's multipurpose test system and multilavel sampling technique on electron micrographs, the nuclear volume density(Vvn) and cytoplasmic volume density(Vvc) were calculated. At the different magnification level established the surface density(Sv) of nucleoid and cell membranes as wel as surface density of rough endoplasmic reticulum and mitochondrial membranes (Svm) and their volume density. Our analysis has confirmed statistically significant increase in Vv of the nucleus of pinealectomized rats. The average volumen of IDC has been also increased after pinealectomy as well as Vv, Nv and Sv of the mitochondria. The present findings seem to support the concept of inhibitory action of pineal gland on thymus IDC.

In this work the authors investigated by qualitative and quantitative analysis of ultrastructural details of thyreocytes in irradiated rats with and without of melatonin treatment. On the basis histological qualitative and stereological analysis of materials and by the comparison of results in the animals who received and who didn't receive melatonin before irradiation it can conclude that melatonin modifies behaviour the thyroid glands in irradiation stress.