The onset of oestrus and ovulation in lactating rats.

نویسندگان

  • R Maneckjee
  • N R Moudgal
چکیده

Lactation delays the re-initiation of oestrous cyclicity in rats, resulting in physiological sterility for the duration of suckling. During this phase, the secretion of pituitary gonadotrophins is suppressed by an unknown mechanism. Continued application of the suckling stimulus by litter replacement (Bruce, 1958; Nicoll & Meites, 1959), or injections of prolactin (Meites & Nicoll, 1959), have been shown to prolong lactation considerably beyond the usual period. The present study aimed to demonstrate the role of prolactin in inhibiting the gonadotrophin secretion necessary for the re-establishment of oestrous cyclicity during lactation. Pregnant rats weighing approximately 300 g were obtained from the Institute colony and housed in individual cages. At parturition, the number of young in the litter was adjusted to eight, two or one as required. The day following the post-partum oestrus was regarded as Day 1 of lactation. The onset of oestrus was confirmed by the presence of cornified epithelial cells in the vaginal smear, and ovulation by the presence of ova in the oviducts at 10.00 hours on the day of oestrus. Oestrus and ovulation occur on Day 22 of lactation in rats suckling eight young each and on Day 16 in those suckling either two or one young each. The data presented in Table 1 show that withdrawal of the young on Days 10 or 14 resulted in the appearance ofoestrus and ovulation 2 days later. Increasing the number of young from two to eight on Day 15 caused a significant post¬ ponement of oestrus and ovulation, but reduction of the size of the litter to two again on Day 16 resulted in postponing oestrus and ovulation only by 1 day. Thus, it is clear that the greater the intensity of suckling, the longer is the dura¬ tion of sterility. Intensity of the suckling stimulus can be directly correlated with an increase in prolactin levels and therefore the effect of giving prolactin to lactating rats on the recurrence of oestrus was studied. Administration of 100 ^g prolactin (ovine prolactin, NIH-P-S9) as a single subcutaneous injection on Day 14 to rats suckling two young each led to a significant delay (from Day 16 to Day 21) in the onset of oestrus and ovulation (Table 2). Injections of prolactin from Days 14 to 16 resulted in a further delay in the re-establishment of cyclicity. A single prolactin injection on Day 20 to lactating rats suckling eight young each postponed oestrus and ovulation from the normal Day 22 to Day 27.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Effect of removing pups when mating lactating rats at the post-partum oestrus.

Rats ovulate during the 1st or 2nd night following parturition (Hoffman & Schwartz, 1965). Subsequently, oestrus is not usually observed during lactation. After weaning, cycling is resumed and only then can oestrus be discerned (Long & Evans, 1922). The possibility of studying the relation between lactation and fertility is, therefore, conditional on effective mating of the females at the post-...

متن کامل

Induction of oestrus and ovulation in anoestrous fallow deer (Dama dama) by using progesterone and GnRH treatment.

Fourteen seasonally anoestrous, non-lactating fallow does were each treated with an intravaginal progesterone device for 14 days followed by a subcutaneously implanted osmotic minipump delivering synthetic GnRH at doses of 125 ng/h (7 does) or 250 ng/h (7 does) for up to 7 days, about 6 weeks before the natural breeding season. One doe (low delivery rate) lost its intravaginal device and 6 of t...

متن کامل

Time of ovulation in nulliparous and multiparous goats.

Fifteen nulliparous and nine multiparous Serrana goats were used, through two successive oestrous cycles, in order to characterize their ovulation time with regard to the number of ovulations after induced and natural oestrus during the breeding season. The onset of oestrus was detected by the amount of vasectomized bucks after oestrus synchronization with prostaglandin, given 10 days apart, an...

متن کامل

Effect of Winter Nutrition and Lactation on Ovulation and Ovulation Rate in Ewes in Autumn

The effect of undernutrition during July-September on oestrus and ovulation rate in Janury-April was investigated in lactating and dry Corriedale ewes. The low levels of nutrition imposed from July resulted in a 5 to 10 kg difference in liveweight in September but thereafter liveweights had equilibrated with control ewes by December. This undernutrition decreased the probability of ovulating ea...

متن کامل

Oestrus, LH, ovulation and fertility in beef heifers.

The pregnancy rate resulting from matings at a single oestrus in beef cattle averages 70% for natural mating (Turman, Laster, Renbarger & Stephens, 1971) and 60% for artificial insemination (Laster, Glimp & Gregory, 1972). The sources and causes of low pregnancy rates have not been defined, but might include variation in time of ovulation relative to deposition of spermatozoa in the female repr...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • Journal of reproduction and fertility

دوره 44 2  شماره 

صفحات  -

تاریخ انتشار 1975