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Biomedical subjects

C H Sawyer

Publications and source records attributed to C H Sawyer.

At least 19 recordsLinked to original sources
PubMed1986

Activation of the CNS noradrenergic system may inhibit as well as facilitate pituitary luteinizing hormone release.

Earlier work established that neural secretion of luteinizing hormone-releasing hormone (LH-RH) and the resultant release of pituitary gonadotropins could be facilitated by activating alpha-receptors of a central noradrenergic (NA) system. The present study emphasizes that central NA mechanisms may also inhibit LH release largely through activation of beta-adrenergic receptors.

Animals↗
PubMed1986

Episodic patterns of luteinizing hormone and follicle-stimulating hormone release: differential secretory dynamics and adrenergic control in ovariectomized rats.

Long term (4 weeks) ovariectomized rats were bled sequentially at 5-min intervals for 5 h via indwelling intraatrial cannulas. Plasma LH and FSH secretory patterns were determined from the same plasma samples by RIA. Hormonal profiles were subjected to power spectral analysis to determine periodicities of plasma LH and FSH. Distinct and regular release patterns were observed for LH, with significant periodicities between 20-40 min. In contrast to LH, FSH oscillations were neither as distinct nor as regular. However, significant periodicities in FSH (50-60 min) were often detected. At times, plasma LH and FSH appeared to be synchronized, but there were numerous instances of differential secretion. The effects of intracerebroventricular infusion of norepinephine (NE) and clonidine (an alpha 2-agonist) were tested in another group of animals. After a 2- to 3-h control bleeding period each animal bearing a chronic third ventricle cannula received an intracerebroventricular infusion of 0.3 mumol NE, clonidine, or vehicle. Blood sampling was continued for 2-3 h after infusion. Intracerebroventricular infusion of NE caused rapid and potent inhibition of LH secretion with FSH affected to a lesser extent. NE infusion decreased mean plasma LH levels and LH pulse amplitude while causing a marked increase in pulse period. Although mean FSH levels declined after NE infusion, secretory episodes of FSH were detectable even in the absence of pulsatile LH secretion. Infusion of an equimolar dose of clonidine produced a biphasic response in LH, a transient elevation followed by a decrease in overall plasma levels. In contrast to LH, plasma FSH levels showed only a delayed decrease after clonidine infusion. No significant changes in pulse amplitude or pulse period for either gonadotropin were observed. These data show that plasma FSH, like LH, oscillates in a periodic manner, but when compared with episodic LH secretion there are both quantitative and qualitative differences. Although the neural mechanisms involved in periodic LH release are also involved to a lesser extent in FSH secretion, it appears that independent regulatory mechanisms exist for LH and FSH as well.

Animals↗
PubMed1979

Effects of transecting lateral neural connections of the medial preoptic area on maternal behavior in the rat: nest building, pup retrieval and prolactin secretion.

In lactating female rats bilateral parasagittal cuts transecting the dorsolateral neural connections of the medial preoptic area (MPOA) abolished nest building and retrieving components of maternal behavior, while crouching and nursing were unaffected. While few animals with these cuts were suckled when presented with pups the prolactin secretion response was undiminished when suckling did occur. Whereas previous studies have demonstrated that extensive surgical separation of the medial preoptic area-anterior hypothalamic continuum from the lateral preoptic area-lateral hypothalamus disrupts all aspects of maternal behavior, the present study has determined more specifically the zone of fibers essential for the active components of maternal behavior, i.e., nest building and retrieving. These fibers appear to enter/leave MPO dorsolaterally beneath the crossing of the anterior commissure in the region of the bed nucleus of the stria terminalis. These neural connections are not the same as those that regulate prolactin secretion in the lactating rat.

Animals↗
PubMed1979

LH release and ovulation in the rat following depletion of hypothalamic norepinephrine: chronic vs. acute effects.

The effects of long-term hypothalamic norepinephrine (NE) depletion on reproductive cyclicity, ovulation, and luteinizing hormone (LH) release were studied in adult female rats. Bilateral transections of the ascending noradrenergic pathway (ANP) at the level of the mesencephalon led to an 83% depletion of hypothalamic NE. Although some animals exhibited a period of acyclicity following this surgical procedure, by 23 days all animals had begun to cycle. When checked for ovulation at around 40 days, all of the rats had shed full quotas of ova. There was no significant difference in either the timing or magnitude of the surge when proestrous LH levels in NE-depleted rats were compared with sham transected controls. To see if the residual hypothalamic NE left after transection of the ascending noradrenergic pathway was important for maintenance of normal LH secretion and ovulation, a group of long-term depleted rats were given an NE synthesis inhibitor (diethyldithiocarbamate: DDC). In all of the sham-cut and intact control rats this drug either partially or completely blocked ovulation, but it was effective in only 40% of the depleted animals. The other 60% not only ovulated, but shed full quotas of ova. These results demonstrate that normal LH secretion can occur even when hyplthalamic NE levels are extremely low. Although acute depressions of NE by pharmacological agents such as DDC effectively block the LH surge, this inhibition is not sustained when NE is depleted over long periods of time. Therefore, NE apparently plays a modulatory, rather than mandatory, role in control of LH release and ovulation.

Animals↗
PubMed1978

Effects of intraventricular injections of norepinephrine on brain-pituitary-ovarian function in the rabbit.

In estrous estrogen-primed female rabbits with electrodes chronically implanted in various subcortical regions of the brain, the intraventricular injection of an ovulation-inducing dose of norepinephrine (NE) stimulated a prolonged episode of high amplitude 40-60 cps electroencephalographic (EEG) activity in the olfactory bulb (OB) and its projections. This activity, which started usually between 30 and 60 min after NE injection and was maintained continously for periods up to an hour thereafter, was regularly absent in the same rabbits when they were pseudopregnant and non-ovulatory to NE. Similar OB-EEG activity and ovulation had been observed earlier in response to intraventricular histamine under light pentobarbital anesthesia. The ovulatory response to histamine was eliminated by massive midbrain lesions or removal of the olfactory bulb, but intraventricular NE still induced ovulation after such losses. The ovulatory effectiveness of NE was blocked, however, by low doses of pentobarbital or high doses of atropine, neither of which inhibited the ovulatory response to intraventricular epinephrine. Atropine and alpha-adrenergic blocking agents also prevented the ovulatory response to intraventricular histamine. It is suggested that histamine activates pituitary-ovarian function by stimulating central noradrenergic elements and that NE has more of the physiological-pharmacological characteristics of a natural central nervous activator of luteinizing hormone-releasing hormone than has epinephrine.

Animals↗
PubMed1978

Changes in diurnal fluctuations of plasma thyroid stimulating hormone and corticosterone following anterior hypothalamic deafferentation in the rat.

Systemic thyroid stimulating hormone (TSH) and corticosterone (B) levels were measured in serial plasma samples withdrawn from 8 adult female rats before and for several weeks after anterior hypothalamic cuts (FC), made with a modified Halász knife (1.5 mm radius). With lights on from 5:00 to 19:00 h the rats were bled by rapid venipuncture at 9:00 and 20:00 h 14 days before and 5 days after FC and by chronic intra-atrial cannulas at 9:00, 13:00, 17:00 and 20:00 h on days 25, 30 and 40 or 50 post-FC. The frontal cuts, localized later by histology to sites just rostral to the suprachiasmatic nucleus in 3 rats and just caudal to the nucleus in the other 5 brains, altered the charactersitic diurnal drop in plasma TSH and rise in B but did not eliminate marked fluctuations in hormone levels. The new hormonal platterns could not be related specifically to FC loci and appeared to be a dynamic process for each rat. At 5 days after FC the diurnal patterns were either obscured or shifted in phase. The most consistent finding at subsequent sampling intervals was that TSH and B plasma levels in each animal showed parallel fluctuations (during 9:00--20:00 h) as though synchronized in phase. The data suggest that interruption of anterior hypothalamic connections in the female rat is compatible with fluctuations in plasma TSH and B which are unique to a particular animal and may be obscured by group analysis.

Afferent Pathways↗
PubMed1977

Electrochemically stimulated release of luteinizing hormone and ovulation after surgical interruption of lateral hypothalamic connections in the rat.

Plasma LH and FSH were studied in adult female rats following bilateral electrochemical stimulation (ECS) of the medial preoptic area (MPOA). By stereotaxic surgery frontal (FC) and frontal-lateral (LFC) retrochiasmatic "deafferenting" cuts were made with a Halász knife (1.5 mm radius). At 3 and 10 weeks after surgery rats were given pentobarbital (32 mg/kg, i.p.) at 13:30h and stimulated at 15:00h with anodal direct current (20 muA for 60 sec) via concentric bipolar steel electrodes placed bilaterally 0.9 mm from the midline. Stimulation at 3 weeks after FC increased plasma LH from a prestimulation level of 95 +/- ng/ml to 227 +/- 51 ng/ml 80 min after ECS, from which it fell to 111 +/- 29 ng/ml at 160 min, with 2 of 7 animals ovulating the next day. LFC females had similar pre-ECS plasma LH levels 3 weeks after surgery (71 +/- 10 ng/ml), but LH concentrations at 80 min (104 +/- 21 ng/ml) and 160 min post-ECS were significantly lower than those of FC rats, and 0 of 5 rats ovulated. Following a similar protocol 10 weeks after surgery, stimulating the MPOA resulted in comparable elevations in plasma LH and 4 of 10 FC animals ovulated; however, the LFC group still retained a significant blocking effect on ovulation (only 1 of 12 ovulated) when compared with controls the next day. Plasma FSH concentrations were not significantly altered by MPOA stimulation at the parameters employed, either before or after deafferentation. However, LFC resulted in reduced ovarian and uterine weights when compared with controls at both 3 and 10 weeks, whereas FC exerted no observable effect on these organs at these intervals of study. The results of these studies suggest that lateral input to the media basal hypothalamus contributes to MPOA mediated release of LH and ovulation as well as to tonic maintenance of ovarian and uterine function.

Animals↗