Cadmium is a heavy metal which is an important industrial raw material and is widely used in batteries, pigments, electroplating, semiconductor and pesticide (Ramos-Treviño M L et al., 2018 and Sall M.L et al., 2020). It is accumulated in the human body with a half-life exceeding 10 years and has been linked with a number of health problems including marked damage to the testes and fertility reduction (Kelley, 1999; Bench et al., 1999). 

Many cadmium-induced changes are similar to those caused by other harmful factors, especially by ionizing radiation. The most striking effects of ionizing radiation include the inhibition of DNA and protein synthesis (Verma et al., 2009). Therefore, with increasing levels of cadmium and radiation in the environment, the biological effects of these agents should be considered in the context of combined exposure of an organism to multiply agents. In the present study, therefore, quantitative analysis of the spermatogonial cell population was investigated in mice testis after administration of cadmium chloride and gamma irradiation alone or after combined treatment.

In the present findings, after cadmium chloride treatment (Group II), the spermatogonia A counts decline up to day 4, then start increasing up to day 28 reaching up to 79.12 percent of the normal counts. This is a similar type of depletion as in the irradiated group, which may be due to cell killing, which leads to an initial rapid decrease in the population of spermatogonia A. Therefore, a gradual decline in their number is found, which continues further due to the death of the damaged cells and more over by spermatogonial differentiation to the more mature types. Similar types of depletions in the population of spermatogonia A were also observed after combined treatment of cadmium chloride and radiation (Group IV) but there was found depletion as compared to respective doses of radiation and cadmium chloride individually. These results have shown an “additive synergistic” type of nature of cadmium chloride with the increased dose of radiation.

Graph I - Variation in the percentage of Spermatogonia  'A'

Graph 2 - Variation in the percentage of Spermatogonia I

Graph 3 - Variation in the percentage of Spermatogonia  B

The response of spermatogonia to various doses of radiation has been investigated by several investigators (Oakberg, 1955a, b; 1959; Oakberg and Diminno, 1960; Monesi, 1962; Oakberg and Clark, 1964). It was evident from all these studies that intermediate and type B spermatogonia in mice were very sensitive to radiation. These were reduced to approximately 0.5 per cent of normal value following 1000 R of x-rays (Oakberg, 1957). It has been observed that type I in stage III and type B in the stage V tubules depleted rapidly and very few could survive after irradiation (Oakberg, 1955a; Monesi 1962b; Parington et al., 1962), cadmium chloride and by the treatment of combined exposure of both. After 48 hours both of these cell types are found to be absent from the tubules at stage III and V respectively in all the experimental groups in our present study. This indicates that irradiation and cadmium chloride inhibit or delay the mitotic division to yield the primary spermatocytes. Both of these spermatogonial types restore a fine percentage of their original number at day 28 in all the experimental groups. This profound recovery in their counts must be due to the re-establishment of cell renewal activity in the stem cell compartment and is a sign of progressing maturation differentiation process.

Oakberg (1968) summarised the comparative radio-sensitivity of various germ cells in the seminiferous epithelium. Oakberg considered spermatogonia B, the most sensitive element of the germinal epithelium.  Spermatogonia I possess a comparable radio sensitivity with spermatogonia B. These findings are almost similar to that observed in the present study. All the types of spermatocytes were also found to be decreased in number after exposure to radiation, cadmium chloride and with combined exposure of both. The number of resting and leptotene spermatocytes decreased at a faster rate than zygotene and pachytene spermatocytes. All these types recovered quantitatively on day 28. Similar observations are made by Sharma (1984) after radiation exposure. Resting and leptotene spermatogonia are highly prone to immediate cadmium and radiation death. 

Direct damage of resting spermatogonia of rats was reported in the dose range of 81-2996 R (Jones, 1960). Casarett and Casarett (1957 a, b) found direct damage to the resting spermatocytes after 283 and 350 R. Death of a small number of resting spermatocytes at 300 R is also noticed by Parington et al. (1962). The division and further differentiation of spermatogonia form the resting primary spermatocytes. So the number of resting primary spermatocytes is directly affected by the damage to the spermatogonia B population. The resting spermatocytes were noted to be the most affected by irradiation after spermatogonia B. They were reduced to zero levels on day 4 and 7 in all the experimental groups in the present study. Depletion in the number of leptotene, zygotene and pachytene spermatocytes was also noted.

Attempts were made by several workers like Monesi (1962), Jaimala and Bhartiya (1985) and Gasinska et al. (1987) to explain the depletion in the number of B type spermatogonia and resting spermatocytes after irradiation. According to them, the decrease is either due to radiation-induced cell death or a lowered output from their precursor compartment. It is evident from graph 2, 3 and 4 the number of spermatogonia I, B and primary resting spermatocytes is significantly lower in the combined sub-groups (IVa, IVb and IVc) as compared to respective irradiated sub-group (IIIa, IIIb and IIIc). This depicts that the cadmium chloride provides synergistic additive action to the spermatogonia I, B and primary resting spermatocytes towards immediate cell killing or radiation injury. The spermatid counts after irradiation (group III) from stage II and III tubules show gradual reduction towards the end of experiments and were found to be dose-dependent. Similar observations were made by other workers (Erickson, 1978; Sharma, 1984; Pinon-Lataillade and Maas, 1985; Jyothi et al., 1998 and Hacker-klom, 2000). Treatment of cadmium chloride and combined action of radiation and cadmium chloride also showed a consistent decline in the percentage of spermatids.

Graph 4 - Variation in the percentage of Resting Spermatocyes

Graph 5 - Variation in the percentage of Leptotene Spermatocytes

Graph 6 - Showing Variation of Percentage of Spermatids