Photoperiod and crowding effects on testicular serotonin metabolism and lack of effects on melatonin synthesis in Uinta ground squirrels (Spermophilus armatus)

Pineal sensitivity to nighttime swimming stress changes during the active season in Richardson's ground squirrels (Spermophilus richardsonii)

Melatonin synthesis in the pineal gland, which is primarily regulated by the environmental lighting regime, can also be influenced by other factors that elicit modifications in sympathetic tone. The objectives of this study were to determine if forced swimming alters the normal pattern of melatonin production in the pineal gland of the Richardson's ground squirrel (Spermophilus richardsonii). In early June, the squirrels were forced to swim for 10 min during the photophase or during the scotophase. In mid-July squirrels swam only during the scotophase. Animals were sacrificed 15, 30, or 60 min after the onset of swimming. Activities of pineal N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) were assessed by radioenzyme assay, and pineal melatonin content was measured by radioimmunoassay. Daytime swimming elicited no major changes in enzyme activity or pineal melatonin. In June, swimming at night prevented the normal rises in NAT activity and pineal melatonin seen in nonswimming controls. In contrast, the pineals of squirrels that were tested 6 weeks later in mid-July did not appear to be as sensitive to nighttime swimming, as there were only minor differences in both NAT activity and melatonin content compared to controls. These results demonstrate that forced nighttime swimming, unlike several other aversive stimuli, can evoke changes in the normal pattern of pineal melatonin production in this species. Furthermore, the pineal's response to such stimuli may not be stable over the course of the active season.

The varicocele: new experimental and clinical data

Numerous reports have shown that serotonin (5-HT) has a detrimental effect on spermatogenesis and androgen synthesis. Serotonin has two mechanisms of action on the testicle: (1) vasoconstrictive changes possibly causing premature sloughing of spermatozoa, and (2) alteration of androgen metabolism. The data in our animals with the experimental varicocele clearly mimic the human situation. All seminal parameters except volume are decreased after the varicocele is created. In many infertile patients with a varicocele, serotonin may be the inciting factor which results in subfertile semen. This is corroborated by the presence of elevated serotonin levels in spermatic vein plasma of most patients with a varicocele who undergo surgery. More data, comparing the relationship between spermatic vein and peripheral blood serotonin levels in patients with and without a varicocele, are needed. This investigation is being pursued in patients undergoing inguinal surgery for other lesions.

The varicocele: elevated serotonin and infertility

Serotonin is known to be toxic to testicular function. In a series of canine studies serotonin was found to be elevated in both spermatic veins after creation of a varicocele by partial ligation of the left renal vein. A total of 42 consecutive infertile male patients with a palpable varicocele and a seminal stress pattern had peripheral and spermatic vein serotonin levels determined at the time of high spermatic vein ligation. Of these patients 27 (64 per cent) had spermatic vein serotonin levels equal to or greater than peripheral levels. These patients demonstrated significantly lower sperm motility, percentage of live sperm and elevated percentages of immature and tapered sperm forms compared to those patients with lower spermatic vein serotonin levels. The interrelationships among the varicocele, premature sloughing of immature sperm and serotonin are discussed.

Inhibition of rat spermatogenesis and seminiferous tubule growth after short-term and long-term administration of a monoamine oxidase inhibitor

Seminiferous tubules from rats killed 24 hours after injection of pargyline, a monoamine oxidase inhibitor, did not grow well in tissue culture when compared to control tubules. Treated tubules showed severe tubular degeneration and loss of cellular detail after nine days in culture. Animals injected with pargyline for ten days had varying degrees of semi-niferous tubule degeneration with depletion of the spermatogenic elements. It is suggested that pargyline has a detrimental effect on spermatogenesis. Pargyline possibly acts by decreasing MAO levels which, in turn, may increase potentially damaging amines which may be responsible for the testicular damage.