Development and Validation of a Simple, Sensitive, Second Antibody Format Enzyme Immunoassay (EIA) for LH Determination in Mithun (Bos Frontalis) Plasma

Effect of age and season on the thyroid hormone activity of Mizoram strain female mithun (Bos frontalis)

AIM

The aim of the present study was to generate baseline data on the normal values of the thyroidhormone (TH) activity as well as their correlation with age and season.

MATERIALS AND METHODS

Blood samples (10 ml) were collected from jugular vein of 30 female mithun's of three different age groups viz. Calves (6 months to 1 year), heifer (1-3 years) and adult (above 3 years) during the three season's viz. Monsoon, winter and spring of a year. The serum was analyzed for thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) activity.

RESULT

The result showed a significantly (p<0.05) a higher T3 level in heifers followed by adults and calves and higher T4 level in adults followed by heifers and calves in all the seasons. The TSH level was higher in heifers in all the seasons. The winter season recorded higher level of T3, T4, and TSH as compared to the other seasons of a year.

CONCLUSION

The TSH and T3 level were the highest for aheifer, whereas T4 level was the highest for adults inall the season. Furthermore, the higher level of TH was observed in winter season. The increased level of the TH during the winter season signifies their calorigenic effect. Similarly in heifers, the increased T3 concentrations show its importance in reproductive physiology and its association with ovarian activity. This indicates that age and season have aprofound effect on TH activity of Mizoram strain female mithun.

Determination of plasma kisspeptin concentrations during reproductive cycle and different phases of pregnancy in crossbred cows using bovine specific enzyme immunoassay

Kisspeptin, a decapeptide and potent secretagogue of GnRH has been emerged recently as a master player in the regulation of reproduction in animals. Determination of kisspeptin in peripheral circulation is, therefore, very important for studying the control of its secretion and its role on reproduction in bovine species, the information on which is not available during any physiological state in this species, may probably be due to non-availability of simple assay procedure to measure the hormone. Therefore, the objective of this study was to develop and validate a simple and sufficiently sensitive enzyme immunoassay (EIA) for kisspeptin determination in bovine plasma using the biotin-streptavidin amplification system and second antibody coating technique. Biotin was coupled to kisspeptin and used to bridge between streptavidin-peroxidase and the immobilized kisspeptin antiserum in the competitive assay. The EIA was conducted directly in 100 μl of unknown bovine plasma. Kisspeptin standards ranging from 0.01 to 25.6 ng/100 μl/well were prepared in hormone-free plasma. The lowest detection limit was 0.1 ng/ml plasma. Plasma volumes for the EIA, viz., 50, 100 and 200 μl did not influence the shape of standard curve even though a drop in OD450 was seen with higher plasma volumes. A parallelism test was carried out to compare the endogenous bovine kisspeptin with kisspeptin standard used. It showed good parallelism with the kisspeptin standard curve. For the biological validation of the assay, plasma kisspeptin was measured in blood samples collected from six non-lactating cyclic cows during entire estrous cycle and from 18 pregnant cows during different stages of pregnancy. The mean plasma kisspeptin concentration during different days of the estrous cycle was different (P<0.001). Three peaks of kisspeptin were recorded, one on a day before appearance of preovulatory LH surge, second at day 6 and third one at day 18 of the estrous cycle. Plasma kisspeptin concentrations increased (P<0.001) from first through last trimester of pregnancy. Kisspeptin concentrations were also measured in different follicular, luteal and placental tissues. Follicular and placental kisspeptin levels increased (P<0.01) during follicular development and with the advancement of pregnancy, respectively. On the other hand, luteal concentrations of kisspeptin decreased (P<0.01) with its developmental process. In conclusion, a simple, sufficiently sensitive and direct EIA procedure has been developed for the first time to determine plasma kisspeptin levels in bovine. A wide range of kisspeptin concentrations can be detected during different physiological stages in bovine using this kisspeptin-EIA procedure.

Development and Application of a Sensitive, Second Antibody Format Enzymeimmunoassay (EIA) for Estimation of Plasma FSH in Mithun (Bos frontalis)

Mithun (Bos frontalis) is a semi-wild rare ruminant species. A simple sensitive enzymeimmunoassay suitable for assaying FSH in the blood plasma of mithun is not available which thereby limits our ability to understand this species reproductive processes. Therefore, the aim of this article was to develop a simple and sensitive enzymeimmunoassay (EIA) for estimation of FSH in mithun plasma and apply the assay to understand the estrous cycle and superovulatory process in this species. To accomplish this goal, biotinylated FSH was bridged between streptavidin-peroxidase and immobilized antiserum in a competitive assay. Forty microlitre mithun plasma was used directly in the EIA. The FSH standards were prepared in hormone free plasma and ranged from 5-1280 pg/well/40 μL. The sensitivity of EIA was 5 pg/well FSH, which corresponds to 0.125 ng/mL plasma and the 50% relative binding sensitivity was 90 pg/well/40 μL. Although the shape of the standard curve was not influenced by different plasma volumes viz. 40 and 80 μL, a slight drop in the OD450 was observed with the increasing volume of plasma. Parallelism tests conducted between the endogenous mithun FSH and bovine FSH standards showed good homology between them. Plasma FSH estimated using the developed EIA and commercially available FSH EIA kit in the same samples were correlated (r = 0.98) and showed linearity. Both the Intra- and inter-assay CV were below 6%. Recovery of known concentrations of added FSH showed linearity (r = 0.99). The developed EIA was further validated biologically by estimating FSH in cyclic cows for the entire estrous cycle, in mithun heifers administered with GnRH analogues and in mithun cows during superovulatory treatment with FSH. In conclusion, the EIA developed for FSH determination in mithun blood plasma is simple and highly sensitive for estimation of mithun FSH in all physiological conditions.

Interaction between salsolinol (SAL) and thyrotropin-releasing hormone (TRH) or dopamine (DA) on the secretion of prolactin in ruminants

We have recently demonstrated that salsolinol (SAL), a dopamine (DA)-derived compound, is present in the posterior pituitary gland and is able to stimulate the release of prolactin (PRL) in ruminants. The aim of the present study was to clarify the effect that the interaction of SAL with thyrotropin-releasing hormone (TRH) or DA has on the secretion of PRL in ruminants. A single intravenous (i.v.) injection of SAL (5mg/kg body weight (b.w.)), TRH (1microg/kg b.w.), and SAL plus TRH significantly stimulated the release of PRL in goats (P<0.05). The cumulative response curve (area under the curve: AUC) during 120min was 1.53 and 1.47 times greater after the injection of SAL plus TRH than either SAL or TRH alone, respectively (P<0.05). A single i.v. injection of sulpiride (a DA receptor antagonist, 0.1mg/kg b.w.), sulpiride plus SAL (5mg/kg b.w.), and sulpiride plus TRH (1microg/kg b.w.) significantly stimulated the release of PRL in goats (P<0.05). The AUC of PRL during 120min was 2.12 and 1.78 times greater after the injection of sulpiride plus TRH than either sulpiride alone or sulpiride plus SAL, respectively (P<0.05). In cultured bovine anterior pituitary (AP) cells, SAL (10(-6)M), TRH (10(-8)M), and SAL plus TRH significantly increased the release of PRL (P<0.05), but the additive effect of SAL and TRH detected in vivo was not observed in vitro. In contrast, DA (10(-6)M) inhibited the TRH-, as well as SAL-induced PRL release in vitro. All together, these results clearly show that SAL can stimulate the release of PRL in ruminants. Furthermore, they also demonstrate that the additive effect of SAL and TRH on the release of PRL detected in vivo may not be mediated at the level of the AP, but that DA can overcome their releasing activity both in vivo and in vitro, confirming the dominant role of DA in the inhibitory regulation of PRL secretion in ruminants.

Salsolinol is present in the bovine posterior pituitary gland and stimulates the release of prolactin both in vivo and in vitro in ruminants

The aims of the present study were to determine whether salsolinol (SAL), a dopamine-related compound, is present in the bovine posterior pituitary (PP) gland, and to clarify the effect of SAL on the secretion of prolactin (PRL) in ruminants. SAL was detected in extract of bovine PP gland using high-pressure liquid chromatography with electrochemical detection (HPLC-EC). A single intravenous (i.v.) injection of SAL (5 and 10mg/kg body weight) significantly and dose-dependently stimulated the release of PRL in goats (P<0.05). Plasma PRL levels reached a peak 10min after the injection, then gradually returned to basal values in 60-80min. The PRL-releasing pattern was similar to that in response to sulpiride (a dopamine receptor antagonist). The intracerebroventricular (i.c.v.) injection of 1mg of SAL had no significant effect on the release of PRL in calves, however, 5mg significantly stimulated the release (P<0.05) with peak values reached 30-40min after the injection. Moreover, SAL significantly stimulated the release of PRL from cultured bovine anterior pituitary cells at doses of 10(-6) and 10(-5)M, compared to control cells (P<0.05). Taken together, our data clearly show that SAL is present in extract of the PP gland of ruminants, and has PRL-releasing activity both in vivo and in vitro. Therefore, this endogenous compound is a strong candidate for the factor having PRL-releasing activity that has been previously detected in extract of the bovine PP gland.

Direct kisspeptin-10 stimulation on luteinizing hormone secretion from bovine and porcine anterior pituitary cells

Kisspeptins are peptide hormones encoded by the KiSS-1 gene and act as the principal positive regulator of the reproductive axis by directly stimulating gonadotropin-releasing hormone (GnRH) neuron activity. However, peripheral administration, as well as central administration, of kisspeptin stimulates luteinizing hormone (LH) secretion in some mammalian species. In order to evaluate the direct effects of kisspeptin-10 (the minimal kisspeptin sequence necessary for receptor activation) on LH secretion from bovine and porcine anterior pituitary (AP) cells, LH-releasing effects of kisspeptin-10 on AP cells were compared with GnRH in vitro. The AP cells were prepared from 1-month-old intact male calves, 8-month-old castrated male calves, or 6-month-old barrows, and then the cells were incubated for 2h with the peptides. The 1000 nM and 10,000 nM, but not lower concentrations, of kisspeptin-10 significantly stimulated LH secretion from the bovine AP cells (P<0.05). The 100 nM and 1000 nM, but not lower concentrations, of kisspeptin-10 significantly stimulated LH secretion from porcine AP cells (P<0.05). As 10nM of GnRH strongly stimulated LH secretion from all AP cells tested in this study, the present results suggest that kisspeptin-10 has a direct, but weak, stimulating effect on LH secretion in bovine and porcine AP cells. The present study is the first to examine the direct actions of kisspeptin on the bovine and porcine pituitary gland as far as we know. Kisspeptin might have other actions on the pituitary because the pituitary has multiple roles.

Oestrous Behaviour and Timing of Ovulation in Relation to Onset of Oestrus and LH Peak in Mithun (Bos frontalis) Cows

The objectives of the study were to evaluate the oestrus behaviour and to determine the timing of ovulation in relation to onset of oestrus and the pre-ovulatory LH surge in mithun (Bos frontalis). For this purpose, the blood samples collected at 15-min intervals for 9 h period following onset of oestrus and thereafter, at an interval of 2 h till 4 h post-ovulation for three consecutive cycles from 12 mithun cows were assayed for plasma LH and progesterone. Ovulation was confirmed by palpation of ovaries per rectum at hourly intervals. Various signs of behavioural oestrus were also recorded. The common signs of oestrus and their frequency of occurrence in mithuns were following and mounting by male mithuns (100%), standing to be mounted (100%), frequent urination (62.33%), raising of tail (65.23%), swelling of vulva (54.26%) and congestion of vulvar mucous membrane (69.87%). The pre-ovulatory LH surges consisted of several pulses (2.92 +/- 0.26 pulses/animal; range, 1-4). The mean (+/-SEM) peak level of LH for individual mithun varied from 6.99 +/- 0.44 to 12.69 +/- 2.10 ng/ml and the mean pooled LH peak concentration was 9.10 +/- 0.60 ng/ml. The highest peak (highest amplitude of LH during LH surge) was 10.83 +/- 0.76 ng/ml (range, 8.07-16.49 ng/ml). The duration of LH surge was 6.98 +/- 0.22 h (6-8 h). Onset of LH surge was at 1.23 +/- 0.17 h post-oestrus onset (range, 0.25-2.25 h). Mean plasma progesterone stayed low (<0.24 ng/ml) during the entire duration of sampling. Ovulation occurred at 26.92 +/- 0.31 (range, 26-29 h) after the onset of oestrus and 18.63 +/- 0.35 h (range, 17-20.75 h) after the end of LH surge. The occurrence of the highest LH peaks within a narrow time frame of 2- to 5-h post-oestrus onset in mithuns could have contributed to the animals ovulating within a narrow time interval. These results are very promising from a practical standpoint of potential success when AI program in this species is implemented in a big way. Furthermore, the results of the occurrence of LH pulses during pre-ovulatory LH surges, which are required for ovulation in this species of animals, is unique and species specific.

Exogenous GH-releasing hormone increases GH and LH secretion in growing mithuns (Bos frontalis)

To investigate the effects of growth hormone-releasing hormone (GHRH) administration on the patterns of GH and LH secretion in growing female mithuns, 12 mithuns within the age group of 10-12 months of age were divided into two groups (treatment and control groups) of six each in such a way that average body weight between the groups did not differ significantly (P>0.05). Both the groups were administered i.v. either with synthetic bGHRH [bGHRH (1-44)-NH2] at 10 microg/100 kg body weight (treatment group) or equal volume of normal saline (control group). Blood samples collected prior to and after GHRH challenge at -60, -45, -30, -15, -10, -5 min and 5, 10, 15, 30 min, and thereafter, at an interval of 15 min up to 8 h post-injection were assayed for plasma GH and LH. Plasma progesterone was estimated in twice-a-week samples collected for six consecutive weeks preceding GHRH challenge to assess whether either group has begun ovarian cyclicity. Body weight of all animals was recorded once in a week during the period. A peak of GH was registered in all animals within 5-25 min post-GHRH administration with a mean peak of 443.5+/-25.32 ng/ml at 15 min post-administration, which was much higher than in any other bovines reported following GHRH challenge. The patterns of LH secretion were pulsatile in nature in both the groups. Interestingly, the hormone concentrations exhibited higher pulsatility with greater amplitude after GHRH challenge in GHRH-treated than in control mithuns. The GHRH-treated mithuns averaged 0.44 pulses/h (4 pulses/9 h) and the rate was 0.20/h (2 pulses/9 h) in controls. The rate of pulse frequency and amplitude differed significantly with time of sampling. The mean plasma LH levels after GHRH administration were significantly higher in treatment group than those recorded in control mithuns. The mean plasma progesterone was similar (P>0.05) in both the groups and no animal from either group had begun ovarian cycle. In conclusion, exogenous GHRH significantly increases plasma GH and also LH pulse frequency and amplitude with higher mean post-GHRH LH levels in growing mithuns suggesting thereby its possible use for enhancement of maturity process in this unique meat animal.

Twenty-four-hour secretion patterns of luteinizing hormone in mithuns (Bos frontalis)

A 24 h secretion pattern of luteinizing hormone (LH) was not available in mithun (Bos frontalis), a semi-wild ruminant. To characterize the 24 h LH profiles, six female mithun calves (age 7.8 +/- 0.5 months and 102.5 +/- 5.6 kg; group I) and six female mithuns averaging 25.4 months of age and 240 kg (group II) were selected from the National Research Centre on Mithun farm and were maintained in semi-intensive systems. Blood samples collected from all the animals at 30 min intervals for 24h were assayed for plasma LH. Plasma progesterone was also estimated in twice-a-week samples collected for 6-week period preceding each 24h sampling to assess whether any animal had begun ovarian cyclicity. The body weights of all animals were also recorded weekly during the 6-week period. LH patterns consisted of frequent pulses of varying amplitude. Luteinizing hormone pulses occurred at an average frequency of 0.28/h ( approximately 7 pulses/24 h) and 0.15/h ( approximately 3.5 pulses/24 h) for mithuns of groups II and I, respectively, the rate did not differ markedly among mithuns within each group but was significantly different between the groups. Similarly, the magnitude of LH secretory pulses did not vary among mithuns within the group but was significantly higher in group II than in group I animals. In group II, the LH peaks averaged 1.59 and 1.00 ng/ml in mithun having the highest and lowest LH peaks, respectively and the corresponding values for group I mithuns were 0.66 and 0.51ng/ml. Mithun with higher peak LH levels also had higher mean LH concentrations (P<0.05). The mithuns of group II had significantly higher plasma progesterone concentration (0.89 +/- 0.02 ng/ml) than those recorded in group I mithuns (0.26 +/- 0.01 ng/ml). Plasma progesterone profiles suggested that no animal reached puberty. In conclusion, there was higher LH secretion with higher pulsatility and greater amplitude in group II mithuns than exhibited in mithuns of group I and the prepubertal mithuns of group II were in approaching puberty, which were also indicated by their plasma progesterone profiles, critical body weight and age required to attain puberty, in addition to higher pulsatility of LH secretion.